20 General utilities library [utilities]
20.1 General [utilities.general]
This Clause describes utilities that are generally useful in C++ programs; some of these utilities are used by other elements of the C++ standard library. These utilities are summarized in Table [tab:util.lib.summary].
| Subclause | Header(s) | |
| [utility] | Utility components | <utility> |
| [pairs] | Pairs | <utility> |
| [tuple] | Tuples | <tuple> |
| [intseq] | Compile-time integer sequences | <utility> |
| [template.bitset] | Fixed-size sequences of bits | <bitset> |
| <memory> | ||
| [memory] | Memory | <cstdlib> |
| <cstring> | ||
| [smartptr] | Smart pointers | <memory> |
| [function.objects] | Function objects | <functional> |
| [meta] | Type traits | <type_traits> |
| [ratio] | Compile-time rational arithmetic | <ratio> |
| [time] | Time utilities | <chrono> |
| <ctime> | ||
| [allocator.adaptor] | Scoped allocators | <scoped_allocator> |
| [type.index] | Type indexes | <typeindex> |
20.2 Utility components [utility]
This subclause contains some basic function and class templates that are used throughout the rest of the library.
The header <utility> defines several types and function templates that are described in this Clause. It also defines the template pair and various function templates that operate on pair objects.
#include <initializer_list>
namespace std {
// [operators], operators:
namespace rel_ops {
template<class T> bool operator!=(const T&, const T&);
template<class T> bool operator> (const T&, const T&);
template<class T> bool operator<=(const T&, const T&);
template<class T> bool operator>=(const T&, const T&);
}
// [utility.swap], swap:
template<class T> void swap(T& a, T& b) noexcept(see below);
template <class T, size_t N> void swap(T (&a)[N], T (&b)[N]) noexcept(noexcept(swap(*a, *b)));
// [utility.exchange], exchange:
template <class T, class U=T> T exchange(T& obj, U&& new_val);
// [forward], forward/move:
template <class T>
constexpr T&& forward(remove_reference_t<T>& t) noexcept;
template <class T>
constexpr T&& forward(remove_reference_t<T>&& t) noexcept;
template <class T>
constexpr remove_reference_t<T>&& move(T&&) noexcept;
template <class T>
constexpr conditional_t<
!is_nothrow_move_constructible<T>::value && is_copy_constructible<T>::value,
const T&, T&&> move_if_noexcept(T& x) noexcept;
// [declval], declval:
template <class T>
add_rvalue_reference_t<T> declval() noexcept; // as unevaluated operand
// [pairs], pairs:
template <class T1, class T2> struct pair;
// [pairs.spec], pair specialized algorithms:
template <class T1, class T2>
constexpr bool operator==(const pair<T1,T2>&, const pair<T1,T2>&);
template <class T1, class T2>
constexpr bool operator< (const pair<T1,T2>&, const pair<T1,T2>&);
template <class T1, class T2>
constexpr bool operator!=(const pair<T1,T2>&, const pair<T1,T2>&);
template <class T1, class T2>
constexpr bool operator> (const pair<T1,T2>&, const pair<T1,T2>&);
template <class T1, class T2>
constexpr bool operator>=(const pair<T1,T2>&, const pair<T1,T2>&);
template <class T1, class T2>
constexpr bool operator<=(const pair<T1,T2>&, const pair<T1,T2>&);
template <class T1, class T2>
void swap(pair<T1,T2>& x, pair<T1,T2>& y) noexcept(noexcept(x.swap(y)));
template <class T1, class T2>
constexpr see below make_pair(T1&&, T2&&);
// [pair.astuple], tuple-like access to pair:
template <class T> class tuple_size;
template <size_t I, class T> class tuple_element;
template <class T1, class T2> struct tuple_size<pair<T1, T2> >;
template <class T1, class T2> struct tuple_element<0, pair<T1, T2> >;
template <class T1, class T2> struct tuple_element<1, pair<T1, T2> >;
template<size_t I, class T1, class T2>
constexpr tuple_element_t<I, pair<T1, T2>>&
get(pair<T1, T2>&) noexcept;
template<size_t I, class T1, class T2>
constexpr tuple_element_t<I, pair<T1, T2>>&&
get(pair<T1, T2>&&) noexcept;
template<size_t I, class T1, class T2>
constexpr const tuple_element_t<I, pair<T1, T2>>&
get(const pair<T1, T2>&) noexcept;
template <class T, class U>
constexpr T& get(pair<T, U>& p) noexcept;
template <class T, class U>
constexpr const T& get(const pair<T, U>& p) noexcept;
template <class T, class U>
constexpr T&& get(pair<T, U>&& p) noexcept;
template <class T, class U>
constexpr T& get(pair<U, T>& p) noexcept;
template <class T, class U>
constexpr const T& get(const pair<U, T>& p) noexcept;
template <class T, class U>
constexpr T&& get(pair<U, T>&& p) noexcept;
// [pair.piecewise], pair piecewise construction
struct piecewise_construct_t { };
constexpr piecewise_construct_t piecewise_construct{};
template <class... Types> class tuple; // defined in <tuple>
// [intseq], Compile-time integer sequences
template<class T, T...> struct integer_sequence;
template<size_t... I>
using index_sequence = integer_sequence<size_t, I...>;
template<class T, T N>
using make_integer_sequence = integer_sequence<T, see below>;
template<size_t N>
using make_index_sequence = make_integer_sequence<size_t, N>;
template<class... T>
using index_sequence_for = make_index_sequence<sizeof...(T)>;
}
20.2.1 Operators [operators]
To avoid redundant definitions of operator!= out of operator== and operators >, <=, and >= out of operator<, the library provides the following:
Requires: Type T is EqualityComparable (Table [equalitycomparable]).
Returns: !(x == y).
template <class T> bool operator>(const T& x, const T& y);
Requires: Type T is LessThanComparable (Table [lessthancomparable]).
Returns: y < x.
template <class T> bool operator<=(const T& x, const T& y);
Requires: Type T is LessThanComparable (Table [lessthancomparable]).
Returns: !(y < x).
template <class T> bool operator>=(const T& x, const T& y);
Requires: Type T is LessThanComparable (Table [lessthancomparable]).
Returns: !(x < y).
In this library, whenever a declaration is provided for an operator!=, operator>, operator>=, or operator<=, and requirements and semantics are not explicitly provided, the requirements and semantics are as specified in this Clause.
20.2.2 swap [utility.swap]
template<class T> void swap(T& a, T& b) noexcept(see below);
Remark: The expression inside noexcept is equivalent to:
is_nothrow_move_constructible<T>::value && is_nothrow_move_assignable<T>::value
Requires: Type T shall be MoveConstructible (Table [moveconstructible]) and MoveAssignable (Table [moveassignable]).
Effects: Exchanges values stored in two locations.
template<class T, size_t N>
void swap(T (&a)[N], T (&b)[N]) noexcept(noexcept(swap(*a, *b)));
Requires: a[i] shall be swappable with ([swappable.requirements]) b[i] for all i in the range [0,N).
Effects: swap_ranges(a, a + N, b)
20.2.3 exchange [utility.exchange]
template <class T, class U=T> T exchange(T& obj, U&& new_val);
Effects: Equivalent to:
T old_val = std::move(obj); obj = std::forward<U>(new_val); return old_val;
20.2.4 forward/move helpers [forward]
The library provides templated helper functions to simplify applying move semantics to an lvalue and to simplify the implementation of forwarding functions.
template <class T> constexpr T&& forward(remove_reference_t<T>& t) noexcept;
template <class T> constexpr T&& forward(remove_reference_t<T>&& t) noexcept;
Returns: static_cast<T&&>(t).
Remark: If the second form is instantiated with an lvalue reference type, the program is ill-formed.
[ Example:
template <class T, class A1, class A2>
shared_ptr<T> factory(A1&& a1, A2&& a2) {
return shared_ptr<T>(new T(std::forward<A1>(a1), std::forward<A2>(a2)));
}
struct A {
A(int&, const double&);
};
void g() {
shared_ptr<A> sp1 = factory<A>(2, 1.414); // error: 2 will not bind to int&
int i = 2;
shared_ptr<A> sp2 = factory<A>(i, 1.414); // OK
}
In the first call to factory, A1 is deduced as int, so 2 is forwarded to A's constructor as an rvalue. In the second call to factory, A1 is deduced as int&, so i is forwarded to A's constructor as an lvalue. In both cases, A2 is deduced as double, so 1.414 is forwarded to A's constructor as an rvalue.
— end example ]
template <class T> constexpr remove_reference_t<T>&& move(T&& t) noexcept;
Returns: static_cast<remove_reference_t<T>&&>(t).
[ Example:
template <class T, class A1>
shared_ptr<T> factory(A1&& a1) {
return shared_ptr<T>(new T(std::forward<A1>(a1)));
}
struct A {
A();
A(const A&); // copies from lvalues
A(A&&); // moves from rvalues
};
void g() {
A a;
shared_ptr<A> sp1 = factory<A>(a); // “a” binds to A(const A&)
shared_ptr<A> sp1 = factory<A>(std::move(a)); // “a” binds to A(A&&)
}
In the first call to factory, A1 is deduced as A&, so a is forwarded as a non-const lvalue. This binds to the constructor A(const A&), which copies the value from a. In the second call to factory, because of the call std::move(a), A1 is deduced as A, so a is forwarded as an rvalue. This binds to the constructor A(A&&), which moves the value from a.
— end example ]
template <class T> constexpr conditional_t<
!is_nothrow_move_constructible<T>::value && is_copy_constructible<T>::value,
const T&, T&&> move_if_noexcept(T& x) noexcept;
Returns: std::move(x)
20.2.5 Function template declval [declval]
The library provides the function template declval to simplify the definition of expressions which occur as unevaluated operands (Clause [expr]).
template <class T>
add_rvalue_reference_t<T> declval() noexcept; // as unevaluated operand
Remarks: If this function is odr-used ([basic.def.odr]), the program is ill-formed.
Remarks: The template parameter T of declval may be an incomplete type.
[ Example:
template <class To, class From> decltype(static_cast<To>(declval<From>())) convert(From&&);
declares a function template convert which only participates in overloading if the type From can be explicitly converted to type To. For another example see class template common_type ([meta.trans.other]). — end example ]
20.3 Pairs [pairs]
20.3.1 In general [pairs.general]
The library provides a template for heterogeneous pairs of values. The library also provides a matching function template to simplify their construction and several templates that provide access to pair objects as if they were tuple objects (see [tuple.helper] and [tuple.elem]).
20.3.2 Class template pair [pairs.pair]
// defined in header <utility> namespace std { template <class T1, class T2> struct pair { typedef T1 first_type; typedef T2 second_type; T1 first; T2 second; pair(const pair&) = default; pair(pair&&) = default; constexpr pair(); constexpr pair(const T1& x, const T2& y); template<class U, class V> constexpr pair(U&& x, V&& y); template<class U, class V> constexpr pair(const pair<U, V>& p); template<class U, class V> constexpr pair(pair<U, V>&& p); template <class... Args1, class... Args2> pair(piecewise_construct_t, tuple<Args1...> first_args, tuple<Args2...> second_args); pair& operator=(const pair& p); template<class U, class V> pair& operator=(const pair<U, V>& p); pair& operator=(pair&& p) noexcept(see below); template<class U, class V> pair& operator=(pair<U, V>&& p); void swap(pair& p) noexcept(see below); }; }
Constructors and member functions of pair shall not throw exceptions unless one of the element-wise operations specified to be called for that operation throws an exception.
The defaulted move and copy constructor, respectively, of pair shall be a constexpr function if and only if all required element-wise initializations for copy and move, respectively, would satisfy the requirements for a constexpr function.
Requires: is_default_constructible<first_type>::value is true
and is_default_construct-
ible<second_type>::value is true.
Effects: Value-initializes first and second.
constexpr pair(const T1& x, const T2& y);
Requires: is_copy_constructible<first_type>::value is true and is_copy_constructible<second_type>::value is true.
Effects: The constructor initializes first with x and second with y.
template<class U, class V> constexpr pair(U&& x, V&& y);
Requires: is_constructible<first_type, U&&>::value is true and is_constructible<second_type, V&&>::value is true.
Effects: The constructor initializes first with std::forward<U>(x) and second with std::forward<V>(y).
Remarks: If U is not implicitly convertible to first_type or V is not implicitly convertible to second_type this constructor shall not participate in overload resolution.
template<class U, class V> constexpr pair(const pair<U, V>& p);
Requires: is_constructible<first_type, const U&>::value is true and is_constructible<second_type, const V&>::value is true.
Effects: Initializes members from the corresponding members of the argument.
Remark: This constructor shall not participate in overload resolution unless const U& is implicitly convertible to first_type and const V& is implicitly convertible to second_type.
template<class U, class V> constexpr pair(pair<U, V>&& p);
Requires: is_constructible<first_type, U&&>::value is true and is_constructible<second_type, V&&>::value is true.
Effects: The constructor initializes first with std::forward<U>(p.first) and second with std::forward<V>(p.second).
Remark: This constructor shall not participate in overload resolution unless U is implicitly convertible to first_type and V is implicitly convertible to second_type.
template<class... Args1, class... Args2>
pair(piecewise_construct_t,
tuple<Args1...> first_args, tuple<Args2...> second_args);
Requires: is_constructible<first_type, Args1&&...>::value is true and is_constructible<second_type, Args2&&...>::value is true.
Effects: The constructor initializes first with arguments of types Args1... obtained by forwarding the elements of first_args and initializes second with arguments of types Args2... obtained by forwarding the elements of second_args. (Here, forwarding an element x of type U within a tuple object means calling std::forward<U>(x).) This form of construction, whereby constructor arguments for first and second are each provided in a separate tuple object, is called piecewise construction.
pair& operator=(const pair& p);
Requires: is_copy_assignable<first_type>::value is true and is_copy_assignable<second_type>::value is true.
Effects: Assigns p.first to first and p.second to second.
Returns: *this.
template<class U, class V> pair& operator=(const pair<U, V>& p);
Requires: is_assignable<first_type&, const U&>::value is true and is_assignable<second_type&, const V&>::value is true.
Effects: Assigns p.first to first and p.second to second.
Returns: *this.
pair& operator=(pair&& p) noexcept(see below);
Remarks: The expression inside noexcept is equivalent to:
is_nothrow_move_assignable<T1>::value && is_nothrow_move_assignable<T2>::value
Requires: is_move_assignable<first_type>::value is true and is_move_assignable<second_type>::value is true.
Effects:
Assigns to first with std::forward<first_type>(p.first)
and to second with
std::forward<second_type>(p.second).
Returns: *this.
template<class U, class V> pair& operator=(pair<U, V>&& p);
Requires: is_assignable<first_type&, U&&>::value is true and is_assignable<second_type&, V&&>::value is true.
Effects:
Assigns to first with std::forward<U>(p.first)
and to second with
std::forward<V>(p.second).
Returns: *this.
void swap(pair& p) noexcept(see below);
Remarks: The expression inside noexcept is equivalent to:
noexcept(swap(first, p.first)) && noexcept(swap(second, p.second))
Requires: first shall be swappable with ([swappable.requirements]) p.first and second shall be swappable with p.second.
Effects: Swaps first with p.first and second with p.second.
20.3.3 Specialized algorithms [pairs.spec]
template <class T1, class T2>
constexpr bool operator==(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: x.first == y.first && x.second == y.second.
template <class T1, class T2>
constexpr bool operator<(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: x.first < y.first || (!(y.first < x.first) && x.second < y.second).
template <class T1, class T2>
constexpr bool operator!=(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: !(x == y)
template <class T1, class T2>
constexpr bool operator>(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: y < x
template <class T1, class T2>
constexpr bool operator>=(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: !(x < y)
template <class T1, class T2>
constexpr bool operator<=(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: !(y < x)
template<class T1, class T2> void swap(pair<T1, T2>& x, pair<T1, T2>& y)
noexcept(noexcept(x.swap(y)));
Effects: x.swap(y)
template <class T1, class T2>
constexpr pair<V1, V2> make_pair(T1&& x, T2&& y);
Returns: pair<V1, V2>(std::forward<T1>(x), std::forward<T2>(y));
where V1 and V2 are determined as follows: Let Ui be decay_t<Ti> for each Ti. Then each Vi is X& if Ui equals reference_wrapper<X>, otherwise Vi is Ui.
[ Example: In place of:
return pair<int, double>(5, 3.1415926); // explicit types
a C++ program may contain:
return make_pair(5, 3.1415926); // types are deduced
— end example ]
20.3.4 Tuple-like access to pair [pair.astuple]
template <class T1, class T2>
struct tuple_size<pair<T1, T2>>
: integral_constant<size_t, 2> { };
tuple_element<0, pair<T1, T2> >::type
Value: the type T1.
tuple_element<1, pair<T1, T2> >::type
Value: the type T2.
template<size_t I, class T1, class T2>
constexpr tuple_element_t<I, pair<T1, T2>>&
get(pair<T1, T2>& p) noexcept;
template<size_t I, class T1, class T2>
constexpr const tuple_element_t<I, pair<T1, T2>>&
get(const pair<T1, T2>& p) noexcept;
Returns: If I == 0 returns p.first; if I == 1 returns p.second; otherwise the program is ill-formed.
template<size_t I, class T1, class T2>
constexpr tuple_element_t<I, pair<T1, T2>>&&
get(pair<T1, T2>&& p) noexcept;
Returns: If I == 0 returns std::forward<T1&&>(p.first); if I == 1 returns std::forward<T2&&>(p.second); otherwise the program is ill-formed.
template <class T, class U>
constexpr T& get(pair<T, U>& p) noexcept;
template <class T, class U>
constexpr const T& get(const pair<T, U>& p) noexcept;
Requires: T and U are distinct types. Otherwise, the program is ill-formed.
Returns: get<0>(p);
template <class T, class U>
constexpr T&& get(pair<T, U>&& p) noexcept;
Requires: T and U are distinct types. Otherwise, the program is ill-formed.
Returns: get<0>(std::move(p));
template <class T, class U>
constexpr T& get(pair<U, T>& p) noexcept;
template <class T, class U>
constexpr const T& get(const pair<U, T>& p) noexcept;
Requires: T and U are distinct types. Otherwise, the program is ill-formed.
Returns: get<1>(p);
template <class T, class U>
constexpr T&& get(pair<U, T>&& p) noexcept;
Requires: T and U are distinct types. Otherwise, the program is ill-formed.
Returns: get<1>(std::move(p));
20.3.5 Piecewise construction [pair.piecewise]
struct piecewise_construct_t { };
constexpr piecewise_construct_t piecewise_construct{};
The struct piecewise_construct_t is an empty structure type used as a unique type to disambiguate constructor and function overloading. Specifically, pair has a constructor with piecewise_construct_t as the first argument, immediately followed by two tuple ([tuple]) arguments used for piecewise construction of the elements of the pair object.
20.4 Tuples [tuple]
20.4.1 In general [tuple.general]
This subclause describes the tuple library that provides a tuple type as the class template tuple that can be instantiated with any number of arguments. Each template argument specifies the type of an element in the tuple. Consequently, tuples are heterogeneous, fixed-size collections of values. An instantiation of tuple with two arguments is similar to an instantiation of pair with the same two arguments. See [pairs].
Header <tuple> synopsis
namespace std {
// [tuple.tuple], class template tuple:
template <class... Types> class tuple;
// [tuple.creation], tuple creation functions:
const unspecified ignore;
template <class... Types>
constexpr tuple<VTypes...> make_tuple(Types&&...);
template <class... Types>
constexpr tuple<Types&&...> forward_as_tuple(Types&&...) noexcept;
template<class... Types>
constexpr tuple<Types&...> tie(Types&...) noexcept;
template <class... Tuples>
constexpr tuple<Ctypes...> tuple_cat(Tuples&&...);
// [tuple.helper], tuple helper classes:
template <class T> class tuple_size; // undefined
template <class T> class tuple_size<const T>;
template <class T> class tuple_size<volatile T>;
template <class T> class tuple_size<const volatile T>;
template <class... Types> class tuple_size<tuple<Types...> >;
template <size_t I, class T> class tuple_element; // undefined
template <size_t I, class T> class tuple_element<I, const T>;
template <size_t I, class T> class tuple_element<I, volatile T>;
template <size_t I, class T> class tuple_element<I, const volatile T>;
template <size_t I, class... Types> class tuple_element<I, tuple<Types...> >;
template <size_t I, class T>
using tuple_element_t = typename tuple_element<I, T>::type;
// [tuple.elem], element access:
template <size_t I, class... Types>
constexpr tuple_element_t<I, tuple<Types...>>&
get(tuple<Types...>&) noexcept;
template <size_t I, class... Types>
constexpr tuple_element_t<I, tuple<Types...>>&&
get(tuple<Types...>&&) noexcept;
template <size_t I, class... Types>
constexpr const tuple_element_t<I, tuple<Types...>>&
get(const tuple<Types...>&) noexcept;
template <class T, class... Types>
constexpr T& get(tuple<Types...>& t) noexcept;
template <class T, class... Types>
constexpr T&& get(tuple<Types...>&& t) noexcept;
template <class T, class... Types>
constexpr const T& get(const tuple<Types...>& t) noexcept;
// [tuple.rel], relational operators:
template<class... TTypes, class... UTypes>
constexpr bool operator==(const tuple<TTypes...>&, const tuple<UTypes...>&);
template<class... TTypes, class... UTypes>
constexpr bool operator<(const tuple<TTypes...>&, const tuple<UTypes...>&);
template<class... TTypes, class... UTypes>
constexpr bool operator!=(const tuple<TTypes...>&, const tuple<UTypes...>&);
template<class... TTypes, class... UTypes>
constexpr bool operator>(const tuple<TTypes...>&, const tuple<UTypes...>&);
template<class... TTypes, class... UTypes>
constexpr bool operator<=(const tuple<TTypes...>&, const tuple<UTypes...>&);
template<class... TTypes, class... UTypes>
constexpr bool operator>=(const tuple<TTypes...>&, const tuple<UTypes...>&);
// [tuple.traits], allocator-related traits
template <class... Types, class Alloc>
struct uses_allocator<tuple<Types...>, Alloc>;
// [tuple.special], specialized algorithms:
template <class... Types>
void swap(tuple<Types...>& x, tuple<Types...>& y) noexcept(see below);
}
20.4.2 Class template tuple [tuple.tuple]
namespace std {
template <class... Types>
class tuple {
public:
// [tuple.cnstr], tuple construction
constexpr tuple();
constexpr explicit tuple(const Types&...);
template <class... UTypes>
constexpr explicit tuple(UTypes&&...);
tuple(const tuple&) = default;
tuple(tuple&&) = default;
template <class... UTypes>
constexpr tuple(const tuple<UTypes...>&);
template <class... UTypes>
constexpr tuple(tuple<UTypes...>&&);
template <class U1, class U2>
constexpr tuple(const pair<U1, U2>&); // only if sizeof...(Types) == 2
template <class U1, class U2>
constexpr tuple(pair<U1, U2>&&); // only if sizeof...(Types) == 2
// allocator-extended constructors
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a);
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a, const Types&...);
template <class Alloc, class... UTypes>
tuple(allocator_arg_t, const Alloc& a, UTypes&&...);
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a, const tuple&);
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a, tuple&&);
template <class Alloc, class... UTypes>
tuple(allocator_arg_t, const Alloc& a, const tuple<UTypes...>&);
template <class Alloc, class... UTypes>
tuple(allocator_arg_t, const Alloc& a, tuple<UTypes...>&&);
template <class Alloc, class U1, class U2>
tuple(allocator_arg_t, const Alloc& a, const pair<U1, U2>&);
template <class Alloc, class U1, class U2>
tuple(allocator_arg_t, const Alloc& a, pair<U1, U2>&&);
// [tuple.assign], tuple assignment
tuple& operator=(const tuple&);
tuple& operator=(tuple&&) noexcept(see below);
template <class... UTypes>
tuple& operator=(const tuple<UTypes...>&);
template <class... UTypes>
tuple& operator=(tuple<UTypes...>&&);
template <class U1, class U2>
tuple& operator=(const pair<U1, U2>&); // only if sizeof...(Types) == 2
template <class U1, class U2>
tuple& operator=(pair<U1, U2>&&); // only if sizeof...(Types) == 2
// [tuple.swap], tuple swap
void swap(tuple&) noexcept(see below);
};
}
20.4.2.1 Construction [tuple.cnstr]
For each tuple constructor, an exception is thrown only if the construction of one of the types in Types throws an exception.
The defaulted move and copy constructor, respectively, of tuple shall be a constexpr function if and only if all required element-wise initializations for copy and move, respectively, would satisfy the requirements for a constexpr function. The defaulted move and copy constructor of tuple<> shall be constexpr functions.
In the constructor descriptions that follow, let i be in the range [0,sizeof...(Types)) in order, Ti be the ith type in Types, and Ui be the ith type in a template parameter pack named UTypes, where indexing is zero-based.
Requires: is_default_constructible<Ti>::value is true for all i.
Effects: Value initializes each element.
constexpr explicit tuple(const Types&...);
Requires: is_copy_constructible<Ti>::value is true for all i.
Effects: Initializes each element with the value of the corresponding parameter.
template <class... UTypes>
constexpr explicit tuple(UTypes&&... u);
Requires: sizeof...(Types) == sizeof...(UTypes). is_constructible<Ti, Ui&&>::value is true for all i.
Effects: Initializes the elements in the tuple with the corresponding value in std::forward<UTypes>(u).
Remark: This constructor shall not participate in overload resolution unless each type in UTypes is implicitly convertible to its corresponding type in Types.
tuple(const tuple& u) = default;
Requires: is_copy_constructible<Ti>::value is true for all i.
Effects: Initializes each element of *this with the corresponding element of u.
Requires: is_move_constructible<Ti>::value is true for all i.
Effects: For all i, initializes the ith element of *this with std::forward<Ti>(get<i>(u)).
template <class... UTypes> constexpr tuple(const tuple<UTypes...>& u);
Requires: sizeof...(Types) == sizeof...(UTypes). is_constructible<Ti, const Ui&>::value is true for all i.
Effects: Constructs each element of *this with the corresponding element of u.
Remark: This constructor shall not participate in overload resolution unless const Ui& is implicitly convertible to Ti for all i.
template <class... UTypes> constexpr tuple(tuple<UTypes...>&& u);
Requires: sizeof...(Types) == sizeof...(UTypes). is_constructible<Ti, Ui&&>::value is true for all i.
Effects: For all i, initializes the ith element of *this with std::forward<Ui>(get<i>(u)).
Remark: This constructor shall not participate in overload resolution unless each type in UTypes is implicitly convertible to its corresponding type in Types.
template <class U1, class U2> constexpr tuple(const pair<U1, U2>& u);
Requires: sizeof...(Types) == 2. is_constructible<T0, const U1&>::value is true for the first type T0 in Types and is_constructible<T1, const U2&>::value is true for the second type T1 in Types.
Effects: Constructs the first element with u.first and the second element with u.second.
Remark: This constructor shall not participate in overload resolution unless const U1& is implicitly convertible to T0 and const U2& is implicitly convertible to T1.
template <class U1, class U2> constexpr tuple(pair<U1, U2>&& u);
Requires: sizeof...(Types) == 2. is_constructible<T0, U1&&>::value is true for the first type T0 in Types and is_constructible<T1, U2&&>::value is true for the second type T1 in Types.
Effects: Initializes the first element with std::forward<U1>(u.first) and the second element with std::forward<U2>(u.second).
Remark: This constructor shall not participate in overload resolution unless U1 is implicitly convertible to T0 and U2 is implicitly convertible to T1.
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a);
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a, const Types&...);
template <class Alloc, class... UTypes>
tuple(allocator_arg_t, const Alloc& a, UTypes&&...);
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a, const tuple&);
template <class Alloc>
tuple(allocator_arg_t, const Alloc& a, tuple&&);
template <class Alloc, class... UTypes>
tuple(allocator_arg_t, const Alloc& a, const tuple<UTypes...>&);
template <class Alloc, class... UTypes>
tuple(allocator_arg_t, const Alloc& a, tuple<UTypes...>&&);
template <class Alloc, class U1, class U2>
tuple(allocator_arg_t, const Alloc& a, const pair<U1, U2>&);
template <class Alloc, class U1, class U2>
tuple(allocator_arg_t, const Alloc& a, pair<U1, U2>&&);
Requires: Alloc shall meet the requirements for an Allocator ([allocator.requirements]).
Effects: Equivalent to the preceding constructors except that each element is constructed with uses-allocator construction ([allocator.uses.construction]).
20.4.2.2 Assignment [tuple.assign]
For each tuple assignment operator, an exception is thrown only if the assignment of one of the types in Types throws an exception. In the function descriptions that follow, let i be in the range [0,sizeof...(Types)) in order, Ti be the ith type in Types, and Ui be the ith type in a template parameter pack named UTypes, where indexing is zero-based.
Requires: is_copy_assignable<Ti>::value is true for all i.
Effects: Assigns each element of u to the corresponding element of *this.
Returns: *this
tuple& operator=(tuple&& u) noexcept(see below);
Remark: The expression inside noexcept is equivalent to the logical and of the following expressions:
is_nothrow_move_assignable<Ti>::value
where Ti is the ith type in Types.
Requires: is_move_assignable<Ti>::value is true for all i.
Effects: For all i, assigns std::forward<Ti>(get<i>(u)) to get<i>(*this).
Returns: *this.
template <class... UTypes>
tuple& operator=(const tuple<UTypes...>& u);
Requires: sizeof...(Types) == sizeof...(UTypes) and is_assignable<Ti&, const Ui&>::value is true for all i.
Effects: Assigns each element of u to the corresponding element of *this.
Returns: *this
template <class... UTypes>
tuple& operator=(tuple<UTypes...>&& u);
Requires:
is_assignable<Ti&, Ui&&>::value == true for all i.
sizeof...(Types) ==
sizeof...(UTypes).
Effects: For all i, assigns std::forward<Ui>(get<i)>(u)) to get<i>(*this).
Returns: *this.
template <class U1, class U2> tuple& operator=(const pair<U1, U2>& u);
Requires: sizeof...(Types) == 2. is_assignable<T0&, const U1&>::value is true for the first type T0 in Types and is_assignable<T1&, const U2&>::value is true for the second type T1 in Types.
Effects: Assigns u.first to the first element of *this and u.second to the second element of *this.
Returns: *this
template <class U1, class U2> tuple& operator=(pair<U1, U2>&& u);
Requires: sizeof...(Types) == 2. is_assignable<T0&, U1&&>::value is true for the first type T0 in Types and is_assignable<T1&, U2&&>::value is true for the second type T1 in Types.
Effects: Assigns std::forward<U1>(u.first) to the first
element of *this and
std::forward<U2>(u.second) to the
second element of *this.
Returns: *this.
20.4.2.3 swap [tuple.swap]
void swap(tuple& rhs) noexcept(see below);
Remark: The expression inside noexcept is equivalent to the logical and of the following expressions:
noexcept(swap(declval<Ti&>>(), declval<Ti&>()))
where Ti is the ith type in Types.
Requires: Each element in *this shall be swappable with ([swappable.requirements]) the corresponding element in rhs.
Effects: Calls swap for each element in *this and its corresponding element in rhs.
Throws: Nothing unless one of the element-wise swap calls throws an exception.
20.4.2.4 Tuple creation functions [tuple.creation]
In the function descriptions that follow, let i be in the range [0,sizeof...(TTypes)) in order and let Ti be the ith type in a template parameter pack named TTypes; let j be in the range [0,sizeof...(UTypes)) in order and Uj be the jth type in a template parameter pack named UTypes, where indexing is zero-based.
template<class... Types>
constexpr tuple<VTypes...> make_tuple(Types&&... t);
Let Ui be decay_t<Ti> for each Ti in Types. Then each Vi in VTypes is X& if Ui equals reference_wrapper<X>, otherwise Vi is Ui.
Returns: tuple<VTypes...>(std::forward<Types>(t)...).
[ Example:
int i; float j; make_tuple(1, ref(i), cref(j))
creates a tuple of type
tuple<int, int&, const float&>
— end example ]
template<class... Types>
constexpr tuple<Types&&...> forward_as_tuple(Types&&... t) noexcept;
Effects: Constructs a tuple of references to the arguments in t suitable for forwarding as arguments to a function. Because the result may contain references to temporary variables, a program shall ensure that the return value of this function does not outlive any of its arguments. (e.g., the program should typically not store the result in a named variable).
Returns: tuple<Types&&...>(std::forward<Types>(t)...)
template<class... Types>
constexpr tuple<Types&...> tie(Types&... t) noexcept;
Returns: tuple<Types&...>(t...). When an argument in t is ignore, assigning any value to the corresponding tuple element has no effect.
[ Example: tie functions allow one to create tuples that unpack tuples into variables. ignore can be used for elements that are not needed:
int i; std::string s;
tie(i, ignore, s) = make_tuple(42, 3.14, "C++");
// i == 42, s == "C++"
— end example ]
template <class... Tuples>
constexpr tuple<CTypes...> tuple_cat(Tuples&&... tpls);
In the following paragraphs, let Ti be the ith type in Tuples, Ui be remove_reference_t<Ti>, and tpi be the ith parameter in the function parameter pack tpls, where all indexing is zero-based.
Requires: For all i, Ui shall be the type cvi tuple<Argsi...>, where cvi is the (possibly empty) ith cv-qualifier-seq and Argsi is the parameter pack representing the element types in Ui. Let Aik be the kith type in Argsi. For all Aik the following requirements shall be satisfied: If Ti is deduced as an lvalue reference type, then is_constructible<Aik, cvi Aik&>::value == true, otherwise is_constructible<Aik, cvi Aik&&>::value == true.
Remarks: The types in Ctypes shall be equal to the ordered sequence of the extended types Args0..., Args1..., ... Argsn-1..., where n is equal to sizeof...(Tuples). Let ei... be the ith ordered sequence of tuple elements of the resulting tuple object corresponding to the type sequence Argsi.
Returns: A tuple object constructed by initializing the kith
type element eik in ei... with
get<ki>(std::forward<Ti>(tpi)) for each valid ki and
each group ei in order.
Note: An implementation may support additional types in the parameter pack Tuples that support the tuple-like protocol, such as pair and array.
20.4.2.5 Tuple helper classes [tuple.helper]
template <class T> struct tuple_size;
Remarks: All specializations of tuple_size<T> shall meet the UnaryTypeTrait requirements ([meta.rqmts]) with a BaseCharacteristic of integral_constant<size_t, N> for some N.
template <class... Types>
class tuple_size<tuple<Types...> >
: public integral_constant<size_t, sizeof...(Types)> { };
template <size_t I, class... Types>
class tuple_element<I, tuple<Types...> > {
public:
typedef TI type;
};
Requires: I < sizeof...(Types). The program is ill-formed if I is out of bounds.
Type: TI is the type of the Ith element of Types, where indexing is zero-based.
template <class T> class tuple_size<const T>;
template <class T> class tuple_size<volatile T>;
template <class T> class tuple_size<const volatile T>;
Let TS denote tuple_size<T> of the cv-unqualified type T. Then each of the three templates shall meet the UnaryTypeTrait requirements ([meta.rqmts]) with a BaseCharacteristic of
integral_constant<size_t, TS::value>
template <size_t I, class T> class tuple_element<I, const T>;
template <size_t I, class T> class tuple_element<I, volatile T>;
template <size_t I, class T> class tuple_element<I, const volatile T>;
Let TE denote tuple_element<I, T> of the cv-unqualified type T. Then each of the three templates shall meet the TransformationTrait requirements ([meta.rqmts]) with a member typedef type that names the following type:
20.4.2.6 Element access [tuple.elem]
template <size_t I, class... Types>
constexpr tuple_element_t<I, tuple<Types...> >& get(tuple<Types...>& t) noexcept;
Requires: I < sizeof...(Types). The program is ill-formed if I is out of bounds.
Returns: A reference to the Ith element of t, where indexing is zero-based.
template <size_t I, class... Types>
constexpr tuple_element_t<I, tuple<Types...> >&& get(tuple<Types...>&& t) noexcept;
Effects: Equivalent to
return std::forward<typename tuple_element<I, tuple<Types...> >
::type&&>(get<I>(t));
Note: if a T in Types is some reference type X&, the return type is X&, not X&&. However, if the element type is a non-reference type T, the return type is T&&.
template <size_t I, class... Types>
constexpr tuple_element_t<I, tuple<Types...> > const& get(const tuple<Types...>& t) noexcept;
Requires: I < sizeof...(Types). The program is ill-formed if I is out of bounds.
Returns: A const reference to the Ith element of t, where indexing is zero-based.
[ Note: Constness is shallow. If a T in Types is some reference type X&, the return type is X&, not const X&. However, if the element type is non-reference type T, the return type is const T&. This is consistent with how constness is defined to work for member variables of reference type. — end note ]
template <class T, class... Types>
constexpr T& get(tuple<Types...>& t) noexcept;
template <class T, class... Types>
constexpr T&& get(tuple<Types...>&& t) noexcept;
template <class T, class... Types>
constexpr const T& get(const tuple<Types...>& t) noexcept;
Requires: The type T occurs exactly once in Types.... Otherwise, the program is ill-formed.
Returns: A reference to the element of t corresponding to the type T in Types....
[ Example:
const tuple<int, const int, double, double> t(1, 2, 3.4, 5.6); const int &i1 = get<int>(t); // OK. Not ambiguous. i1 == 1 const int &i2 = get<const int>(t); // OK. Not ambiguous. i2 == 2 const double &d = get<double>(t); // ERROR. ill-formed
— end example ]
[ Note: The reason get is a nonmember function is that if this functionality had been provided as a member function, code where the type depended on a template parameter would have required using the template keyword. — end note ]
20.4.2.7 Relational operators [tuple.rel]
template<class... TTypes, class... UTypes>
constexpr bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
Requires: For all i, where 0 <= i and i < sizeof...(TTypes), get<i>(t) == get<i>(u) is a valid expression returning a type that is convertible to bool. sizeof...(TTypes) == sizeof...(UTypes).
Returns: true if get<i>(t) == get<i>(u) for all i, otherwise false. For any two zero-length tuples e and f, e == f returns true.
Effects: The elementary comparisons are performed in order from the zeroth index upwards. No comparisons or element accesses are performed after the first equality comparison that evaluates to false.
template<class... TTypes, class... UTypes>
constexpr bool operator<(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
Requires: For all i, where 0 <= i and i < sizeof...(TTypes), get<i>(t) < get<i>(u) and get<i>(u) < get<i>(t) are valid expressions returning types that are convertible to bool. sizeof...(TTypes) == sizeof...(UTypes).
Returns: The result of a lexicographical comparison between t and u. The result is defined as: (bool)(get<0>(t) < get<0>(u)) || (!(bool)(get<0>(u) < get<0>(t)) && ttail < utail), where rtail for some tuple r is a tuple containing all but the first element of r. For any two zero-length tuples e and f, e < f returns false.
template<class... TTypes, class... UTypes>
constexpr bool operator!=(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
Returns: !(t == u).
template<class... TTypes, class... UTypes>
constexpr bool operator>(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
Returns: u < t.
template<class... TTypes, class... UTypes>
constexpr bool operator<=(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
Returns: !(u < t)
template<class... TTypes, class... UTypes>
constexpr bool operator>=(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
Returns: !(t < u)
[ Note: The above definitions for comparison operators do not require ttail (or utail) to be constructed. It may not even be possible, as t and u are not required to be copy constructible. Also, all comparison operators are short circuited; they do not perform element accesses beyond what is required to determine the result of the comparison. — end note ]
20.4.2.8 Tuple traits [tuple.traits]
template <class... Types, class Alloc>
struct uses_allocator<tuple<Types...>, Alloc> : true_type { };
Requires: Alloc shall be an Allocator ([allocator.requirements]).
[ Note: Specialization of this trait informs other library components that tuple can be constructed with an allocator, even though it does not have a nested allocator_type. — end note ]
20.4.2.9 Tuple specialized algorithms [tuple.special]
template <class... Types>
void swap(tuple<Types...>& x, tuple<Types...>& y) noexcept(see below);
Remark: The expression inside noexcept is equivalent to:
noexcept(x.swap(y))
Effects: x.swap(y)
20.5 Compile-time integer sequences [intseq]
20.5.1 In general [intseq.general]
The library provides a class template that can represent an integer sequence. When used as an argument to a function template the parameter pack defining the sequence can be deduced and used in a pack expansion.
[ Example:
template<class F, class Tuple, std::size_t... I>
decltype(auto) apply_impl(F&& f, Tuple&& t, index_sequence<I...>) {
return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
}
template<class F, class Tuple>
decltype(auto) apply(F&& f, Tuple&& t) {
using Indices = make_index_sequence<std::tuple_size<std::decay_t<Tuple>>::value>;
return apply_impl(std::forward<F>(f), std::forward<Tuple>(t), Indices());
}
— end example ] [ Note: The index_sequence alias template is provided for the common case of an integer sequence of type size_t. — end note ]
20.5.2 Class template integer_sequence [intseq.intseq]
namespace std {
template<class T, T... I>
struct integer_sequence {
typedef T value_type;
static constexpr size_t size() noexcept { return sizeof...(I); }
};
}
T shall be an integer type.
20.5.3 Alias template make_integer_sequence [intseq.make]
template<class T, T N>
using make_integer_sequence = integer_sequence<T, see below>;
If N is negative the program is ill-formed. The alias template make_integer_sequence denotes a specialization of integer_sequence with N template non-type arguments. The type make_integer_sequence<T, N> denotes the type integer_sequence<T, 0, 1, ..., N-1>. [ Note: make_integer_sequence<int, 0> denotes the type integer_sequence<int> — end note ]
20.6 Class template bitset [template.bitset]
#include <string> #include <iosfwd> // for istream, ostream namespace std { template <size_t N> class bitset; // [bitset.operators] bitset operators: template <size_t N> bitset<N> operator&(const bitset<N>&, const bitset<N>&) noexcept; template <size_t N> bitset<N> operator|(const bitset<N>&, const bitset<N>&) noexcept; template <size_t N> bitset<N> operator^(const bitset<N>&, const bitset<N>&) noexcept; template <class charT, class traits, size_t N> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& is, bitset<N>& x); template <class charT, class traits, size_t N> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const bitset<N>& x); }
The header <bitset> defines a class template and several related functions for representing and manipulating fixed-size sequences of bits.
namespace std {
template<size_t N> class bitset {
public:
// bit reference:
class reference {
friend class bitset;
reference() noexcept;
public:
~reference() noexcept;
reference& operator=(bool x) noexcept; // for b[i] = x;
reference& operator=(const reference&) noexcept; // for b[i] = b[j];
bool operator~() const noexcept; // flips the bit
operator bool() const noexcept; // for x = b[i];
reference& flip() noexcept; // for b[i].flip();
};
// [bitset.cons] constructors:
constexpr bitset() noexcept;
constexpr bitset(unsigned long long val) noexcept;
template<class charT, class traits, class Allocator>
explicit bitset(
const basic_string<charT,traits,Allocator>& str,
typename basic_string<charT,traits,Allocator>::size_type pos = 0,
typename basic_string<charT,traits,Allocator>::size_type n =
basic_string<charT,traits,Allocator>::npos,
charT zero = charT('0'), charT one = charT('1'));
template <class charT>
explicit bitset(
const charT* str,
typename basic_string<charT>::size_type n = basic_string<charT>::npos,
charT zero = charT('0'), charT one = charT('1'));
// [bitset.members] bitset operations:
bitset<N>& operator&=(const bitset<N>& rhs) noexcept;
bitset<N>& operator|=(const bitset<N>& rhs) noexcept;
bitset<N>& operator^=(const bitset<N>& rhs) noexcept;
bitset<N>& operator<<=(size_t pos) noexcept;
bitset<N>& operator>>=(size_t pos) noexcept;
bitset<N>& set() noexcept;
bitset<N>& set(size_t pos, bool val = true);
bitset<N>& reset() noexcept;
bitset<N>& reset(size_t pos);
bitset<N> operator~() const noexcept;
bitset<N>& flip() noexcept;
bitset<N>& flip(size_t pos);
// element access:
constexpr bool operator[](size_t pos) const; // for b[i];
reference operator[](size_t pos); // for b[i];
unsigned long to_ulong() const;
unsigned long long to_ullong() const;
template <class charT = char,
class traits = char_traits<charT>,
class Allocator = allocator<charT> >
basic_string<charT, traits, Allocator>
to_string(charT zero = charT('0'), charT one = charT('1')) const;
size_t count() const noexcept;
constexpr size_t size() const noexcept;
bool operator==(const bitset<N>& rhs) const noexcept;
bool operator!=(const bitset<N>& rhs) const noexcept;
bool test(size_t pos) const;
bool all() const noexcept;
bool any() const noexcept;
bool none() const noexcept;
bitset<N> operator<<(size_t pos) const noexcept;
bitset<N> operator>>(size_t pos) const noexcept;
};
// [bitset.hash] hash support
template <class T> struct hash;
template <size_t N> struct hash<bitset<N> >;
}
The class template bitset<N>describes an object that can store a sequence consisting of a fixed number of bits, N.
Each bit represents either the value zero (reset) or one (set). To toggle a bit is to change the value zero to one, or the value one to zero. Each bit has a non-negative position pos. When converting between an object of class bitset<N> and a value of some integral type, bit position pos corresponds to the bit value 1 << pos. The integral value corresponding to two or more bits is the sum of their bit values.
The functions described in this subclause can report three kinds of errors, each associated with a distinct exception:
an invalid-argument error is associated with exceptions of type invalid_argument ([invalid.argument]);
an out-of-range error is associated with exceptions of type out_of_range ([out.of.range]);
an overflow error is associated with exceptions of type overflow_error ([overflow.error]).
20.6.1 bitset constructors [bitset.cons]
Effects: Constructs an object of class bitset<N>, initializing all bits to zero.
constexpr bitset(unsigned long long val) noexcept;
Effects: Constructs an object of class bitset<N>, initializing the first M bit positions to the corresponding bit values in val. M is the smaller of N and the number of bits in the value representation ([basic.types]) of unsigned long long. If M < N, the remaining bit positions are initialized to zero.
template <class charT, class traits, class Allocator>
explicit
bitset(const basic_string<charT, traits, Allocator>& str,
typename basic_string<charT, traits, Allocator>::size_type pos = 0,
typename basic_string<charT, traits, Allocator>::size_type n =
basic_string<charT, traits, Allocator>::npos,
charT zero = charT('0'), charT one = charT('1'));
Requires: pos <= str.size().
Effects: Determines the effective length rlen of the initializing string as the smaller of n and str.size() - pos.
The function then throws invalid_argument if any of the rlen characters in str beginning at position pos is other than zero or one. The function uses traits::eq() to compare the character values.
Otherwise, the function constructs an object of class bitset<N>, initializing the first M bit positions to values determined from the corresponding characters in the string str. M is the smaller of N and rlen.
An element of the constructed object has value zero if the corresponding character in str, beginning at position pos, is zero. Otherwise, the element has the value one. Character position pos + M - 1 corresponds to bit position zero. Subsequent decreasing character positions correspond to increasing bit positions.
If M < N, remaining bit positions are initialized to zero.
template <class charT>
explicit bitset(
const charT* str,
typename basic_string<charT>::size_type n = basic_string<charT>::npos,
charT zero = charT('0'), charT one = charT('1'));
Effects: Constructs an object of class bitset<N> as if by
bitset(
n == basic_string<charT>::npos
? basic_string<charT>(str)
: basic_string<charT>(str, n),
0, n, zero, one)
20.6.2 bitset members [bitset.members]
bitset<N>& operator&=(const bitset<N>& rhs) noexcept;
Effects: Clears each bit in *this for which the corresponding bit in rhs is clear, and leaves all other bits unchanged.
Returns: *this.
bitset<N>& operator|=(const bitset<N>& rhs) noexcept;
Effects: Sets each bit in *this for which the corresponding bit in rhs is set, and leaves all other bits unchanged.
Returns: *this.
bitset<N>& operator^=(const bitset<N>& rhs) noexcept;
Effects: Toggles each bit in *this for which the corresponding bit in rhs is set, and leaves all other bits unchanged.
Returns: *this.
bitset<N>& operator<<=(size_t pos) noexcept;
Returns: *this.
bitset<N>& operator>>=(size_t pos) noexcept;
Returns: *this.
Effects: Sets all bits in *this.
Returns: *this.
bitset<N>& set(size_t pos, bool val = true);
Requires: pos is valid
Effects: Stores a new value in the bit at position pos in *this. If val is nonzero, the stored value is one, otherwise it is zero.
Returns: *this.
Effects: Resets all bits in *this.
Returns: *this.
Requires: pos is valid
Effects: Resets the bit at position pos in *this.
Returns: *this.
bitset<N> operator~() const noexcept;
Effects: Constructs an object x of class bitset<N> and initializes it with *this.
Returns: x.flip().
Effects: Toggles all bits in *this.
Returns: *this.
Requires: pos is valid
Effects: Toggles the bit at position pos in *this.
Returns: *this.
unsigned long to_ulong() const;
Returns: x.
unsigned long long to_ullong() const;
Returns: x.
template <class charT = char,
class traits = char_traits<charT>,
class Allocator = allocator<charT> >
basic_string<charT, traits, Allocator>
to_string(charT zero = charT('0'), charT one = charT('1')) const;
Effects: Constructs a string object of the appropriate type and initializes it to a string of length N characters. Each character is determined by the value of its corresponding bit position in *this. Character position N - 1 corresponds to bit position zero. Subsequent decreasing character positions correspond to increasing bit positions. Bit value zero becomes the character zero, bit value one becomes the character one.
Returns: The created object.
size_t count() const noexcept;
Returns: A count of the number of bits set in *this.
constexpr size_t size() const noexcept;
Returns: N.
bool operator==(const bitset<N>& rhs) const noexcept;
Returns: true if the value of each bit in *this equals the value of the corresponding bit in rhs.
bool operator!=(const bitset<N>& rhs) const noexcept;
Returns: true if !(*this == rhs).
Requires: pos is valid
Returns: true if the bit at position pos in *this has the value one.
Returns: count() == size()
Returns: count() != 0
Returns: count() == 0
bitset<N> operator<<(size_t pos) const noexcept;
Returns: bitset<N>(*this) <<= pos.
bitset<N> operator>>(size_t pos) const noexcept;
Returns: bitset<N>(*this) >>= pos.
constexpr bool operator[](size_t pos) const;
Requires: pos shall be valid.
Returns: true if the bit at position pos in *this has the value one, otherwise false.
Throws: Nothing.
bitset<N>::reference operator[](size_t pos);
Requires: pos shall be valid.
Returns: An object of type bitset<N>::reference such that (*this)[pos] == this->test(pos), and such that (*this)[pos] = val is equivalent to this->set(pos, val).
Throws: Nothing.
Remark: For the purpose of determining the presence of a data race ([intro.multithread]), any access or update through the resulting reference potentially accesses or modifies, respectively, the entire underlying bitset.
20.6.3 bitset hash support [bitset.hash]
template <size_t N> struct hash<bitset<N> >;
The template specialization shall meet the requirements of class template hash ([unord.hash]).
20.6.4 bitset operators [bitset.operators]
bitset<N> operator&(const bitset<N>& lhs, const bitset<N>& rhs) noexcept;
Returns: bitset<N>(lhs) &= rhs.
bitset<N> operator|(const bitset<N>& lhs, const bitset<N>& rhs) noexcept;
Returns: bitset<N>(lhs) |= rhs.
bitset<N> operator^(const bitset<N>& lhs, const bitset<N>& rhs) noexcept;
Returns: bitset<N>(lhs) ^= rhs.
template <class charT, class traits, size_t N>
basic_istream<charT, traits>&
operator>>(basic_istream<charT, traits>& is, bitset<N>& x);
A formatted input function ([istream.formatted]).
Effects: Extracts up to N characters from is. Stores these characters in a temporary object str of type basic_string<charT, traits>, then evaluates the expression x = bitset<N>(str). Characters are extracted and stored until any of the following occurs:
If no characters are stored in str, calls is.setstate(ios_base::failbit) (which may throw ios_base::failure ([iostate.flags])).
Returns: is.
template <class charT, class traits, size_t N>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const bitset<N>& x);
Returns:
os << x.template to_string<charT,traits,allocator<charT> >(
use_facet<ctype<charT> >(os.getloc()).widen('0'),
use_facet<ctype<charT> >(os.getloc()).widen('1'))
(see [ostream.formatted]).
20.7 Memory [memory]
20.7.1 In general [memory.general]
This subclause describes the contents of the header <memory> ([memory.syn]) and some of the contents of the C headers <cstdlib> and <cstring> ([c.malloc]).
20.7.2 Header <memory> synopsis [memory.syn]
The header <memory> defines several types and function templates that describe properties of pointers and pointer-like types, manage memory for containers and other template types, and construct multiple objects in uninitialized memory buffers ([pointer.traits]–[specialized.algorithms]). The header also defines the templates unique_ptr, shared_ptr, weak_ptr, and various function templates that operate on objects of these types ([smartptr]).
namespace std {
// [pointer.traits], pointer traits
template <class Ptr> struct pointer_traits;
template <class T> struct pointer_traits<T*>;
// [util.dynamic.safety], pointer safety
enum class pointer_safety { relaxed, preferred, strict };
void declare_reachable(void* p);
template <class T> T* undeclare_reachable(T* p);
void declare_no_pointers(char* p, size_t n);
void undeclare_no_pointers(char* p, size_t n);
pointer_safety get_pointer_safety() noexcept;
// [ptr.align], pointer alignment function
void* align(std::size_t alignment, std::size_t size,
void*& ptr, std::size_t& space);
// [allocator.tag], allocator argument tag
struct allocator_arg_t { };
constexpr allocator_arg_t allocator_arg{};
// [allocator.uses], uses_allocator
template <class T, class Alloc> struct uses_allocator;
// [allocator.traits], allocator traits
template <class Alloc> struct allocator_traits;
// [default.allocator], the default allocator:
template <class T> class allocator;
template <> class allocator<void>;
template <class T, class U>
bool operator==(const allocator<T>&, const allocator<U>&) noexcept;
template <class T, class U>
bool operator!=(const allocator<T>&, const allocator<U>&) noexcept;
// [storage.iterator], raw storage iterator:
template <class OutputIterator, class T> class raw_storage_iterator;
// [temporary.buffer], temporary buffers:
template <class T>
pair<T*,ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
template <class T>
void return_temporary_buffer(T* p);
// [specialized.algorithms], specialized algorithms:
template <class T> T* addressof(T& r) noexcept;
template <class InputIterator, class ForwardIterator>
ForwardIterator uninitialized_copy(InputIterator first, InputIterator last,
ForwardIterator result);
template <class InputIterator, class Size, class ForwardIterator>
ForwardIterator uninitialized_copy_n(InputIterator first, Size n,
ForwardIterator result);
template <class ForwardIterator, class T>
void uninitialized_fill(ForwardIterator first, ForwardIterator last,
const T& x);
template <class ForwardIterator, class Size, class T>
ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n, const T& x);
// [unique.ptr] class template unique_ptr:
template <class T> struct default_delete;
template <class T> struct default_delete<T[]>;
template <class T, class D = default_delete<T>> class unique_ptr;
template <class T, class D> class unique_ptr<T[], D>;
template <class T, class... Args> unique_ptr<T> make_unique(Args&&... args);
template <class T> unique_ptr<T> make_unique(size_t n);
template <class T, class... Args> unspecified make_unique(Args&&...) = delete;
template <class T, class D> void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y) noexcept;
template <class T1, class D1, class T2, class D2>
bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template <class T1, class D1, class T2, class D2>
bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template <class T1, class D1, class T2, class D2>
bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template <class T1, class D1, class T2, class D2>
bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template <class T1, class D1, class T2, class D2>
bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template <class T1, class D1, class T2, class D2>
bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template <class T, class D>
bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
template <class T, class D>
bool operator==(nullptr_t, const unique_ptr<T, D>& y) noexcept;
template <class T, class D>
bool operator!=(const unique_ptr<T, D>& x, nullptr_t) noexcept;
template <class T, class D>
bool operator!=(nullptr_t, const unique_ptr<T, D>& y) noexcept;
template <class T, class D>
bool operator<(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator<(nullptr_t, const unique_ptr<T, D>& y);
template <class T, class D>
bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator<=(nullptr_t, const unique_ptr<T, D>& y);
template <class T, class D>
bool operator>(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator>(nullptr_t, const unique_ptr<T, D>& y);
template <class T, class D>
bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator>=(nullptr_t, const unique_ptr<T, D>& y);
// [util.smartptr.weakptr], class bad_weak_ptr:
class bad_weak_ptr;
// [util.smartptr.shared], class template shared_ptr:
template<class T> class shared_ptr;
// [util.smartptr.shared.create], shared_ptr creation
template<class T, class... Args> shared_ptr<T> make_shared(Args&&... args);
template<class T, class A, class... Args>
shared_ptr<T> allocate_shared(const A& a, Args&&... args);
// [util.smartptr.shared.cmp], shared_ptr comparisons:
template<class T, class U>
bool operator==(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
template<class T, class U>
bool operator!=(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
template<class T, class U>
bool operator<(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
template<class T, class U>
bool operator>(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
template<class T, class U>
bool operator<=(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
template<class T, class U>
bool operator>=(shared_ptr<T> const& a, shared_ptr<U> const& b) noexcept;
template <class T>
bool operator==(const shared_ptr<T>& x, nullptr_t) noexcept;
template <class T>
bool operator==(nullptr_t, const shared_ptr<T>& y) noexcept;
template <class T>
bool operator!=(const shared_ptr<T>& x, nullptr_t) noexcept;
template <class T>
bool operator!=(nullptr_t, const shared_ptr<T>& y) noexcept;
template <class T>
bool operator<(const shared_ptr<T>& x, nullptr_t) noexcept;
template <class T>
bool operator<(nullptr_t, const shared_ptr<T>& y) noexcept;
template <class T>
bool operator<=(const shared_ptr<T>& x, nullptr_t) noexcept;
template <class T>
bool operator<=(nullptr_t, const shared_ptr<T>& y) noexcept;
template <class T>
bool operator>(const shared_ptr<T>& x, nullptr_t) noexcept;
template <class T>
bool operator>(nullptr_t, const shared_ptr<T>& y) noexcept;
template <class T>
bool operator>=(const shared_ptr<T>& x, nullptr_t) noexcept;
template <class T>
bool operator>=(nullptr_t, const shared_ptr<T>& y) noexcept;
// [util.smartptr.shared.spec], shared_ptr specialized algorithms:
template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b) noexcept;
// [util.smartptr.shared.cast], shared_ptr casts:
template<class T, class U>
shared_ptr<T> static_pointer_cast(shared_ptr<U> const& r) noexcept;
template<class T, class U>
shared_ptr<T> dynamic_pointer_cast(shared_ptr<U> const& r) noexcept;
template<class T, class U>
shared_ptr<T> const_pointer_cast(shared_ptr<U> const& r) noexcept;
// [util.smartptr.getdeleter], shared_ptr get_deleter:
template<class D, class T> D* get_deleter(shared_ptr<T> const& p) noexcept;
// [util.smartptr.shared.io], shared_ptr I/O:
template<class E, class T, class Y>
basic_ostream<E, T>& operator<< (basic_ostream<E, T>& os, shared_ptr<Y> const& p);
// [util.smartptr.weak], class template weak_ptr:
template<class T> class weak_ptr;
// [util.smartptr.weak.spec], weak_ptr specialized algorithms:
template<class T> void swap(weak_ptr<T>& a, weak_ptr<T>& b) noexcept;
// [util.smartptr.ownerless], class template owner_less:
template<class T> class owner_less;
// [util.smartptr.enab], class template enable_shared_from_this:
template<class T> class enable_shared_from_this;
// [util.smartptr.shared.atomic], shared_ptr atomic access:
template<class T>
bool atomic_is_lock_free(const shared_ptr<T>* p);
template<class T>
shared_ptr<T> atomic_load(const shared_ptr<T>* p);
template<class T>
shared_ptr<T> atomic_load_explicit(const shared_ptr<T>* p, memory_order mo);
template<class T>
void atomic_store(shared_ptr<T>* p, shared_ptr<T> r);
template<class T>
void atomic_store_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);
template<class T>
shared_ptr<T> atomic_exchange(shared_ptr<T>* p, shared_ptr<T> r);
template<class T>
shared_ptr<T> atomic_exchange_explicit(shared_ptr<T>* p, shared_ptr<T> r,
memory_order mo);
template<class T>
bool atomic_compare_exchange_weak(
shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
template<class T>
bool atomic_compare_exchange_strong(
shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
template<class T>
bool atomic_compare_exchange_weak_explicit(
shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
memory_order success, memory_order failure);
template<class T>
bool atomic_compare_exchange_strong_explicit(
shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
memory_order success, memory_order failure);
// [util.smartptr.hash] hash support
template <class T> struct hash;
template <class T, class D> struct hash<unique_ptr<T, D> >;
template <class T> struct hash<shared_ptr<T> >;
// [depr.auto.ptr], auto_ptr (deprecated)
template <class X> class auto_ptr;
}
20.7.3 Pointer traits [pointer.traits]
The class template pointer_traits supplies a uniform interface to certain attributes of pointer-like types.
namespace std {
template <class Ptr> struct pointer_traits {
typedef Ptr pointer;
typedef see below element_type;
typedef see below difference_type;
template <class U> using rebind = see below;
static pointer pointer_to(see below r);
};
template <class T> struct pointer_traits<T*> {
typedef T* pointer;
typedef T element_type;
typedef ptrdiff_t difference_type;
template <class U> using rebind = U*;
static pointer pointer_to(see below r) noexcept;
};
}
20.7.3.1 Pointer traits member types [pointer.traits.types]
typedef see below element_type;
Type: Ptr::element_type if such a type exists; otherwise, T if Ptr is a class template instantiation of the form SomePointer<T, Args>, where Args is zero or more type arguments; otherwise, the specialization is ill-formed.
typedef see below difference_type;
Type: Ptr::difference_type if such a type exists; otherwise, std::ptrdiff_t.
template <class U> using rebind = see below;
Alias template: Ptr::rebind<U> if such a type exists; otherwise, SomePointer<U, Args> if Ptr is a class template instantiation of the form SomePointer<T, Args>, where Args is zero or more type arguments; otherwise, the instantiation of rebind is ill-formed.
20.7.3.2 Pointer traits member functions [pointer.traits.functions]
static pointer pointer_traits::pointer_to(see below r);
static pointer pointer_traits<T*>::pointer_to(see below r) noexcept;
Remark: If element_type is (possibly cv-qualified) void, the type of r is unspecified; otherwise, it is element_type&.
Returns: The first member function returns a pointer to r obtained by calling Ptr::pointer_to(r) through which indirection is valid; an instantiation of this function is ill-formed if Ptr does not have a matching pointer_to static member function. The second member function returns std::addressof(r).
20.7.4 Pointer safety [util.dynamic.safety]
A complete object is declared reachable while the number of calls to declare_reachable with an argument referencing the object exceeds the number of calls to undeclare_reachable with an argument referencing the object.
Requires: p shall be a safely-derived pointer ([basic.stc.dynamic.safety]) or a null pointer value.
Effects: If p is not null, the complete object referenced by p is subsequently declared reachable ([basic.stc.dynamic.safety]).
Throws: May throw std::bad_alloc if the system cannot allocate additional memory that may be required to track objects declared reachable.
template <class T> T* undeclare_reachable(T* p);
Requires: If p is not null, the complete object referenced by p shall have been previously declared reachable, and shall be live ([basic.life]) from the time of the call until the last undeclare_reachable(p) call on the object.
Returns: A safely derived copy of p which shall compare equal to p.
Throws: Nothing.
[ Note: It is expected that calls to declare_reachable(p) will consume a small amount of memory in addition to that occupied by the referenced object until the matching call to undeclare_reachable(p) is encountered. Long running programs should arrange that calls are matched. — end note ]
void declare_no_pointers(char* p, size_t n);
Requires: No bytes in the specified range are currently registered with declare_no_pointers(). If the specified range is in an allocated object, then it must be entirely within a single allocated object. The object must be live until the corresponding undeclare_no_pointers() call. [ Note: In a garbage-collecting implementation, the fact that a region in an object is registered with declare_no_pointers() should not prevent the object from being collected. — end note ]
Effects: The n bytes starting at p no longer contain traceable pointer locations, independent of their type. Hence indirection through a pointer located there is undefined if the object it points to was created by global operator new and not previously declared reachable. [ Note: This may be used to inform a garbage collector or leak detector that this region of memory need not be traced. — end note ]
Throws: Nothing.
[ Note: Under some conditions implementations may need to allocate memory. However, the request can be ignored if memory allocation fails. — end note ]
void undeclare_no_pointers(char* p, size_t n);
Requires: The same range must previously have been passed to declare_no_pointers().
Effects: Unregisters a range registered with declare_no_pointers() for destruction. It must be called before the lifetime of the object ends.
Throws: Nothing.
pointer_safety get_pointer_safety() noexcept;
Returns: pointer_safety::strict if the implementation has strict pointer safety ([basic.stc.dynamic.safety]). It is implementation defined whether get_pointer_safety returns pointer_safety::relaxed or pointer_safety::preferred if the implementation has relaxed pointer safety.230
pointer_safety::preferred might be returned to indicate that a leak detector is running so that the program can avoid spurious leak reports.
20.7.5 Align [ptr.align]
void* align(std::size_t alignment, std::size_t size,
void*& ptr, std::size_t& space);
Effects: If it is possible to fit size bytes of storage aligned by alignment into the buffer pointed to by ptr with length space, the function updates ptr to point to the first possible address of such storage and decreases space by the number of bytes used for alignment. Otherwise, the function does nothing.
Returns: A null pointer if the requested aligned buffer would not fit into the available space, otherwise the adjusted value of ptr.
[ Note: The function updates its ptr and space arguments so that it can be called repeatedly with possibly different alignment and size arguments for the same buffer. — end note ]
20.7.6 Allocator argument tag [allocator.tag]
namespace std {
struct allocator_arg_t { };
constexpr allocator_arg_t allocator_arg{};
}
The allocator_arg_t struct is an empty structure type used as a unique type to disambiguate constructor and function overloading. Specifically, several types (see tuple [tuple]) have constructors with allocator_arg_t as the first argument, immediately followed by an argument of a type that satisfies the Allocator requirements ([allocator.requirements]).
20.7.7 uses_allocator [allocator.uses]
20.7.7.1 uses_allocator trait [allocator.uses.trait]
template <class T, class Alloc> struct uses_allocator;
Remark: automatically detects whether T has a nested allocator_type that is convertible from Alloc. Meets the BinaryTypeTrait requirements ([meta.rqmts]). The implementation shall provide a definition that is derived from true_type if a type T::allocator_type exists and is_convertible<Alloc, T::allocator_type>::value != false, otherwise it shall be derived from false_type. A program may specialize this template to derive from true_type for a user-defined type T that does not have a nested allocator_type but nonetheless can be constructed with an allocator where either:
the first argument of a constructor has type allocator_arg_t and the second argument has type Alloc or
the last argument of a constructor has type Alloc.
20.7.7.2 uses-allocator construction [allocator.uses.construction]
Uses-allocator construction with allocator Alloc refers to the construction of an object obj of type T, using constructor arguments v1, v2, ..., vN of types V1, V2, ..., VN, respectively, and an allocator alloc of type Alloc, according to the following rules:
if uses_allocator<T, Alloc>::value is false and is_constructible<T, V1, V2, ..., VN>::value is true, then obj is initialized as obj(v1, v2, ..., vN);
otherwise, if uses_allocator<T, Alloc>::value is true and is_constructible<T, allocator_arg_t, Alloc, V1, V2, ..., VN>::value is true, then obj is initialized as obj(allocator_arg, alloc, v1, v2, ..., vN);
otherwise, if uses_allocator<T, Alloc>::value is true and is_constructible<T, V1, V2, ..., VN, Alloc>::value is true, then obj is initialized as obj(v1, v2, ..., vN, alloc);
otherwise, the request for uses-allocator construction is ill-formed. [ Note: An error will result if uses_allocator<T, Alloc>::value is true but the specific constructor does not take an allocator. This definition prevents a silent failure to pass the allocator to an element. — end note ]
20.7.8 Allocator traits [allocator.traits]
The class template allocator_traits supplies a uniform interface to all allocator types. An allocator cannot be a non-class type, however, even if allocator_traits supplies the entire required interface. [ Note: Thus, it is always possible to create a derived class from an allocator. — end note ]
namespace std {
template <class Alloc> struct allocator_traits {
typedef Alloc allocator_type;
typedef typename Alloc::value_type value_type;
typedef see below pointer;
typedef see below const_pointer;
typedef see below void_pointer;
typedef see below const_void_pointer;
typedef see below difference_type;
typedef see below size_type;
typedef see below propagate_on_container_copy_assignment;
typedef see below propagate_on_container_move_assignment;
typedef see below propagate_on_container_swap;
template <class T> using rebind_alloc = see below;
template <class T> using rebind_traits = allocator_traits<rebind_alloc<T> >;
static pointer allocate(Alloc& a, size_type n);
static pointer allocate(Alloc& a, size_type n, const_void_pointer hint);
static void deallocate(Alloc& a, pointer p, size_type n);
template <class T, class... Args>
static void construct(Alloc& a, T* p, Args&&... args);
template <class T>
static void destroy(Alloc& a, T* p);
static size_type max_size(const Alloc& a) noexcept;
static Alloc select_on_container_copy_construction(const Alloc& rhs);
};
}
20.7.8.1 Allocator traits member types [allocator.traits.types]
Type: Alloc::pointer if such a type exists; otherwise, value_type*.
typedef see below const_pointer;
Type: Alloc::const_pointer if such a type exists; otherwise, pointer_traits<pointer>::rebind<const value_type>.
typedef see below void_pointer;
Type: Alloc::void_pointer if such a type exists; otherwise, pointer_traits<pointer>::rebind<void>.
typedef see below const_void_pointer;
Type: Alloc::const_void_pointer if such a type exists; otherwise, pointer_traits<pointer>::rebind<const void>.
typedef see below difference_type;
Type: Alloc::difference_type if such a type exists; otherwise, pointer_traits<pointer>::difference_type.
Type: Alloc::size_type if such a type exists; otherwise, make_unsigned_t<difference_type>.
typedef see below propagate_on_container_copy_assignment;
Type: Alloc::propagate_on_container_copy_assignment if such a type exists, otherwise false_type.
typedef see below propagate_on_container_move_assignment;
Type: Alloc::propagate_on_container_move_assignment if such a type exists, otherwise false_type.
typedef see below propagate_on_container_swap;
Type: Alloc::propagate_on_container_swap if such a type exists, otherwise false_type.
template <class T> using rebind_alloc = see below;
Alias template: Alloc::rebind<T>::other if such a type exists; otherwise, Alloc<T, Args> if Alloc is a class template instantiation of the form Alloc<U, Args>, where Args is zero or more type arguments; otherwise, the instantiation of rebind_alloc is ill-formed.
20.7.8.2 Allocator traits static member functions [allocator.traits.members]
static pointer allocate(Alloc& a, size_type n);
Returns: a.allocate(n).
static pointer allocate(Alloc& a, size_type n, const_void_pointer hint);
Returns: a.allocate(n, hint) if that expression is well-formed; otherwise, a.allocate(n).
static void deallocate(Alloc& a, pointer p, size_type n);
Effects: calls a.deallocate(p, n).
Throws: Nothing.
template <class T, class... Args>
static void construct(Alloc& a, T* p, Args&&... args);
Effects: calls a.construct(p, std::forward<Args>(args)...) if that call is well-formed; otherwise, invokes ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...).
template <class T>
static void destroy(Alloc& a, T* p);
Effects: calls a.destroy(p) if that call is well-formed; otherwise, invokes p->~T().
static size_type max_size(const Alloc& a) noexcept;
Returns: a.max_size() if that expression is well-formed; otherwise, numeric_limits<size_type>::max().
static Alloc select_on_container_copy_construction(const Alloc& rhs);
Returns: rhs.select_on_container_copy_construction() if that expression is well-formed; otherwise, rhs.
20.7.9 The default allocator [default.allocator]
namespace std {
template <class T> class allocator;
// specialize for void:
template <> class allocator<void> {
public:
typedef void* pointer;
typedef const void* const_pointer;
// reference-to-void members are impossible.
typedef void value_type;
template <class U> struct rebind { typedef allocator<U> other; };
};
template <class T> class allocator {
public:
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef T* pointer;
typedef const T* const_pointer;
typedef T& reference;
typedef const T& const_reference;
typedef T value_type;
template <class U> struct rebind { typedef allocator<U> other; };
typedef true_type propagate_on_container_move_assignment;
allocator() noexcept;
allocator(const allocator&) noexcept;
template <class U> allocator(const allocator<U>&) noexcept;
~allocator();
pointer address(reference x) const noexcept;
const_pointer address(const_reference x) const noexcept;
pointer allocate(
size_type, allocator<void>::const_pointer hint = 0);
void deallocate(pointer p, size_type n);
size_type max_size() const noexcept;
template<class U, class... Args>
void construct(U* p, Args&&... args);
template <class U>
void destroy(U* p);
};
}
20.7.9.1 allocator members [allocator.members]
Except for the destructor, member functions of the default allocator shall not introduce data races ([intro.multithread]) as a result of concurrent calls to those member functions from different threads. Calls to these functions that allocate or deallocate a particular unit of storage shall occur in a single total order, and each such deallocation call shall happen before the next allocation (if any) in this order.
Returns: The actual address of the object referenced by x, even in the presence of an overloaded operator&.
const_pointer address(const_reference x) const noexcept;
Returns: The actual address of the object referenced by x, even in the presence of an overloaded operator&.
pointer allocate(size_type n, allocator<void>::const_pointer hint = 0);
[ Note: In a container member function, the address of an adjacent element is often a good choice to pass for the hint argument. — end note ]
Returns: A pointer to the initial element of an array of storage of size n * sizeof(T), aligned appropriately for objects of type T. It is implementation-defined whether over-aligned types are supported ([basic.align]).
Remark: the storage is obtained by calling ::operator new(std::size_t) ([new.delete]), but it is unspecified when or how often this function is called. The use of hint is unspecified, but intended as an aid to locality if an implementation so desires.
Throws: bad_alloc if the storage cannot be obtained.
void deallocate(pointer p, size_type n);
Requires: p shall be a pointer value obtained from allocate(). n shall equal the value passed as the first argument to the invocation of allocate which returned p.
Effects: Deallocates the storage referenced by p .
Remarks: Uses ::operator delete(void*, std::size_t) ([new.delete]), but it is unspecified when this function is called.
size_type max_size() const noexcept;
Returns: The largest value N for which the call allocate(N,0) might succeed.
template <class U, class... Args>
void construct(U* p, Args&&... args);
Effects: ::new((void *)p) U(std::forward<Args>(args)...)
template <class U>
void destroy(U* p);
Effects: p->~U()
20.7.9.2 allocator globals [allocator.globals]
template <class T1, class T2>
bool operator==(const allocator<T1>&, const allocator<T2>&) noexcept;
Returns: true.
template <class T1, class T2>
bool operator!=(const allocator<T1>&, const allocator<T2>&) noexcept;
Returns: false.
20.7.10 Raw storage iterator [storage.iterator]
raw_storage_iterator is provided to enable algorithms to store their results into uninitialized memory. The template parameter OutputIterator is required to have its operator* return an object for which operator& is defined and returns a pointer to T, and is also required to satisfy the requirements of an output iterator ([output.iterators]).
namespace std {
template <class OutputIterator, class T>
class raw_storage_iterator
: public iterator<output_iterator_tag,void,void,void,void> {
public:
explicit raw_storage_iterator(OutputIterator x);
raw_storage_iterator& operator*();
raw_storage_iterator& operator=(const T& element);
raw_storage_iterator& operator++();
raw_storage_iterator operator++(int);
};
}
Effects: Initializes the iterator to point to the same value to which x points.
raw_storage_iterator& operator*();
Returns: *this
raw_storage_iterator& operator=(const T& element);
Effects: Constructs a value from element at the location to which the iterator points.
Returns: A reference to the iterator.
raw_storage_iterator& operator++();
Effects: Pre-increment: advances the iterator and returns a reference to the updated iterator.
raw_storage_iterator operator++(int);
Effects: Post-increment: advances the iterator and returns the old value of the iterator.
20.7.11 Temporary buffers [temporary.buffer]
template <class T>
pair<T*, ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
Effects: Obtains a pointer to storage sufficient to store up to n adjacent T objects. It is implementation-defined whether over-aligned types are supported ([basic.align]).
Returns: A pair containing the buffer's address and capacity (in the units of sizeof(T)), or a pair of 0 values if no storage can be obtained or if n <= 0.
template <class T> void return_temporary_buffer(T* p);
Effects: Deallocates the buffer to which p points.
Requires: The buffer shall have been previously allocated by get_temporary_buffer.
20.7.12 Specialized algorithms [specialized.algorithms]
All the iterators that are used as template parameters in the following algorithms are required to have their operator* return an object for which operator& is defined and returns a pointer to T. In the algorithm uninitialized_copy, the template parameter InputIterator is required to satisfy the requirements of an input iterator ([input.iterators]). In all of the following algorithms, the template parameter ForwardIterator is required to satisfy the requirements of a forward iterator ([forward.iterators]), and is required to have the property that no exceptions are thrown from increment, assignment, comparison, or indirection through valid iterators. In the following algorithms, if an exception is thrown there are no effects.
20.7.12.1 addressof [specialized.addressof]
template <class T> T* addressof(T& r) noexcept;
Returns: The actual address of the object or function referenced by r, even in the presence of an overloaded operator&.
20.7.12.2 uninitialized_copy [uninitialized.copy]
template <class InputIterator, class ForwardIterator>
ForwardIterator uninitialized_copy(InputIterator first, InputIterator last,
ForwardIterator result);
Effects:
for (; first != last; ++result, ++first)
::new (static_cast<void*>(&*result))
typename iterator_traits<ForwardIterator>::value_type(*first);
Returns: result
template <class InputIterator, class Size, class ForwardIterator>
ForwardIterator uninitialized_copy_n(InputIterator first, Size n,
ForwardIterator result);
Effects:
for ( ; n > 0; ++result, ++first, --n) {
::new (static_cast<void*>(&*result))
typename iterator_traits<ForwardIterator>::value_type(*first);
}
Returns: result
20.7.12.3 uninitialized_fill [uninitialized.fill]
template <class ForwardIterator, class T>
void uninitialized_fill(ForwardIterator first, ForwardIterator last,
const T& x);
Effects:
for (; first != last; ++first)
::new (static_cast<void*>(&*first))
typename iterator_traits<ForwardIterator>::value_type(x);
20.7.12.4 uninitialized_fill_n [uninitialized.fill.n]
template <class ForwardIterator, class Size, class T>
ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n, const T& x);
Effects:
for (; n--; ++first)
::new (static_cast<void*>(&*first))
typename iterator_traits<ForwardIterator>::value_type(x);
return first;
20.7.13 C library [c.malloc]
Table [tab:util.hdr.cstdlib] describes the header <cstdlib>.
The contents are the same as the Standard C library header <stdlib.h>, with the following changes:
The functions calloc(), malloc(), and realloc() do not attempt to allocate storage by calling ::operator new() ([support.dynamic]).
The function free() does not attempt to deallocate storage by calling ::operator delete().
See also: ISO C Clause 7.11.2.
Storage allocated directly with malloc(), calloc(), or realloc() is implicitly declared reachable (see [basic.stc.dynamic.safety]) on allocation, ceases to be declared reachable on deallocation, and need not cease to be declared reachable as the result of an undeclare_reachable() call. [ Note: This allows existing C libraries to remain unaffected by restrictions on pointers that are not safely derived, at the expense of providing far fewer garbage collection and leak detection options for malloc()-allocated objects. It also allows malloc() to be implemented with a separate allocation arena, bypassing the normal declare_reachable() implementation. The above functions should never intentionally be used as a replacement for declare_reachable(), and newly written code is strongly encouraged to treat memory allocated with these functions as though it were allocated with operator new. — end note ]
Table [tab:util.hdr.cstring] describes the header <cstring>.
| Type | Name(s) | |
| Macro: | NULL | |
| Type: | size_t | |
| Functions: | memchr | memcmp |
| memcpy | memmove | memset |
The contents are the same as the Standard C library header <string.h>, with the change to memchr() specified in [c.strings].
See also: ISO C Clause 7.11.2.
20.8 Smart pointers [smartptr]
20.8.1 Class template unique_ptr [unique.ptr]
A unique pointer is an object that owns another object and manages that other object through a pointer. More precisely, a unique pointer is an object u that stores a pointer to a second object p and will dispose of p when u is itself destroyed (e.g., when leaving block scope ([stmt.dcl])). In this context, u is said to own p.
The mechanism by which u disposes of p is known as p's associated deleter, a function object whose correct invocation results in p's appropriate disposition (typically its deletion).
Let the notation u.p denote the pointer stored by u, and let u.d denote the associated deleter. Upon request, u can reset (replace) u.p and u.d with another pointer and deleter, but must properly dispose of its owned object via the associated deleter before such replacement is considered completed.
Additionally, u can, upon request, transfer ownership to another unique pointer u2. Upon completion of such a transfer, the following postconditions hold:
u2.p is equal to the pre-transfer u.p,
u.p is equal to nullptr, and
if the pre-transfer u.d maintained state, such state has been transferred to u2.d.
As in the case of a reset, u2 must properly dispose of its pre-transfer owned object via the pre-transfer associated deleter before the ownership transfer is considered complete. [ Note: A deleter's state need never be copied, only moved or swapped as ownership is transferred. — end note ]
Each object of a type U instantiated from the unique_ptr template specified in this subclause has the strict ownership semantics, specified above, of a unique pointer. In partial satisfaction of these semantics, each such U is MoveConstructible and MoveAssignable, but is not CopyConstructible nor CopyAssignable. The template parameter T of unique_ptr may be an incomplete type.
[ Note: The uses of unique_ptr include providing exception safety for dynamically allocated memory, passing ownership of dynamically allocated memory to a function, and returning dynamically allocated memory from a function. — end note ]
namespace std {
template<class T> struct default_delete;
template<class T> struct default_delete<T[]>;
template<class T, class D = default_delete<T>> class unique_ptr;
template<class T, class D> class unique_ptr<T[], D>;
template<class T, class... Args> unique_ptr<T> make_unique(Args&&... args);
template<class T> unique_ptr<T> make_unique(size_t n);
template<class T, class... Args> unspecified make_unique(Args&&...) = delete;
template<class T, class D> void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y) noexcept;
template<class T1, class D1, class T2, class D2>
bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template<class T1, class D1, class T2, class D2>
bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template<class T1, class D1, class T2, class D2>
bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template<class T1, class D1, class T2, class D2>
bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template<class T1, class D1, class T2, class D2>
bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template<class T1, class D1, class T2, class D2>
bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
template <class T, class D>
bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
template <class T, class D>
bool operator==(nullptr_t, const unique_ptr<T, D>& y) noexcept;
template <class T, class D>
bool operator!=(const unique_ptr<T, D>& x, nullptr_t) noexcept;
template <class T, class D>
bool operator!=(nullptr_t, const unique_ptr<T, D>& y) noexcept;
template <class T, class D>
bool operator<(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator<(nullptr_t, const unique_ptr<T, D>& y);
template <class T, class D>
bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator<=(nullptr_t, const unique_ptr<T, D>& y);
template <class T, class D>
bool operator>(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator>(nullptr_t, const unique_ptr<T, D>& y);
template <class T, class D>
bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator>=(nullptr_t, const unique_ptr<T, D>& y);
}
20.8.1.1 Default deleters [unique.ptr.dltr]
20.8.1.1.1 In general [unique.ptr.dltr.general]
The class template default_delete serves as the default deleter (destruction policy) for the class template unique_ptr.
The template parameter T of default_delete may be an incomplete type.
20.8.1.1.2 default_delete [unique.ptr.dltr.dflt]
namespace std {
template <class T> struct default_delete {
constexpr default_delete() noexcept = default;
template <class U> default_delete(const default_delete<U>&) noexcept;
void operator()(T*) const;
};
}
template <class U> default_delete(const default_delete<U>& other) noexcept;
Effects: Constructs a default_delete object from another default_delete<U> object.
Remarks: This constructor shall not participate in overload resolution unless U* is implicitly convertible to T*.
void operator()(T* ptr) const;
Effects: calls delete on ptr.
Remarks: If T is an incomplete type, the program is ill-formed.
20.8.1.1.3 default_delete<T[]> [unique.ptr.dltr.dflt1]
namespace std {
template <class T> struct default_delete<T[]> {
constexpr default_delete() noexcept = default;
void operator()(T*) const;
template <class U> void operator()(U*) const = delete;
};
}
void operator()(T* ptr) const;
Effects: calls delete[] on ptr.
Remarks: If T is an incomplete type, the program is ill-formed.
20.8.1.2 unique_ptr for single objects [unique.ptr.single]
namespace std {
template <class T, class D = default_delete<T>> class unique_ptr {
public:
typedef see below pointer;
typedef T element_type;
typedef D deleter_type;
// [unique.ptr.single.ctor], constructors
constexpr unique_ptr() noexcept;
explicit unique_ptr(pointer p) noexcept;
unique_ptr(pointer p, see below d1) noexcept;
unique_ptr(pointer p, see below d2) noexcept;
unique_ptr(unique_ptr&& u) noexcept;
constexpr unique_ptr(nullptr_t) noexcept
: unique_ptr() { }
template <class U, class E>
unique_ptr(unique_ptr<U, E>&& u) noexcept;
template <class U>
unique_ptr(auto_ptr<U>&& u) noexcept;
// [unique.ptr.single.dtor], destructor
~unique_ptr();
// [unique.ptr.single.asgn], assignment
unique_ptr& operator=(unique_ptr&& u) noexcept;
template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
unique_ptr& operator=(nullptr_t) noexcept;
// [unique.ptr.single.observers], observers
add_lvalue_reference_t<T> operator*() const;
pointer operator->() const noexcept;
pointer get() const noexcept;
deleter_type& get_deleter() noexcept;
const deleter_type& get_deleter() const noexcept;
explicit operator bool() const noexcept;
// [unique.ptr.single.modifiers] modifiers
pointer release() noexcept;
void reset(pointer p = pointer()) noexcept;
void swap(unique_ptr& u) noexcept;
// disable copy from lvalue
unique_ptr(const unique_ptr&) = delete;
unique_ptr& operator=(const unique_ptr&) = delete;
};
}
The default type for the template parameter D is default_delete. A client-supplied template argument D shall be a function object type ([function.objects]), lvalue-reference to function, or lvalue-reference to function object type for which, given a value d of type D and a value ptr of type unique_ptr<T, D>::pointer, the expression d(ptr) is valid and has the effect of disposing of the pointer as appropriate for that deleter.
If the deleter's type D is not a reference type, D shall satisfy the requirements of Destructible (Table [destructible]).
If the type remove_reference_t<D>::pointer exists, then unique_ptr<T, D>::pointer shall be a synonym for remove_reference_t<D>::pointer. Otherwise unique_ptr<T, D>::pointer shall be a synonym for T*. The type unique_ptr<T, D>::pointer shall satisfy the requirements of NullablePointer ([nullablepointer.requirements]).
[ Example: Given an allocator type X ([allocator.requirements]) and letting A be a synonym for allocator_traits<X>, the types A::pointer, A::const_pointer, A::void_pointer, and A::const_void_pointer may be used as unique_ptr<T, D>::pointer. — end example ]
20.8.1.2.1 unique_ptr constructors [unique.ptr.single.ctor]
constexpr unique_ptr() noexcept;
Requires: D shall satisfy the requirements of DefaultConstructible (Table [defaultconstructible]), and that construction shall not throw an exception.
Effects: Constructs a unique_ptr object that owns nothing, value-initializing the stored pointer and the stored deleter.
Postconditions: get() == nullptr. get_deleter() returns a reference to the stored deleter.
Remarks: If this constructor is instantiated with a pointer type or reference type for the template argument D, the program is ill-formed.
explicit unique_ptr(pointer p) noexcept;
Requires: D shall satisfy the requirements of DefaultConstructible (Table [defaultconstructible]), and that construction shall not throw an exception.
Effects: Constructs a unique_ptr which owns p, initializing the stored pointer with p and value-initializing the stored deleter.
Postconditions: get() == p. get_deleter() returns a reference to the stored deleter.
Remarks: If this constructor is instantiated with a pointer type or reference type for the template argument D, the program is ill-formed.
unique_ptr(pointer p, see below d1) noexcept;
unique_ptr(pointer p, see below d2) noexcept;
The signature of these constructors depends upon whether D is a reference type. If D is non-reference type A, then the signatures are:
unique_ptr(pointer p, const A& d); unique_ptr(pointer p, A&& d);
If D is an lvalue-reference type A&, then the signatures are:
unique_ptr(pointer p, A& d); unique_ptr(pointer p, A&& d);
If D is an lvalue-reference type const A&, then the signatures are:
unique_ptr(pointer p, const A& d); unique_ptr(pointer p, const A&& d);
Requires:
If D is not an lvalue-reference type then
If d is an lvalue or const rvalue then the first constructor of this pair will be selected. D shall satisfy the requirements of CopyConstructible (Table [copyconstructible]), and the copy constructor of D shall not throw an exception. This unique_ptr will hold a copy of d.
Otherwise, d is a non-const rvalue and the second constructor of this pair will be selected. D shall satisfy the requirements of MoveConstructible (Table [moveconstructible]), and the move constructor of D shall not throw an exception. This unique_ptr will hold a value move constructed from d.
Otherwise D is an lvalue-reference type. d shall be reference-compatible with one of the constructors. If d is an rvalue, it will bind to the second constructor of this pair and the program is ill-formed. [ Note: The diagnostic could be implemented using a static_assert which assures that D is not a reference type. — end note ] Else d is an lvalue and will bind to the first constructor of this pair. The type which D references need not be CopyConstructible nor MoveConstructible. This unique_ptr will hold a D which refers to the lvalue d. [ Note: D may not be an rvalue-reference type. — end note ]
Effects: Constructs a unique_ptr object which owns p, initializing the stored pointer with p and initializing the deleter as described above.
Postconditions: get() == p. get_deleter() returns a reference to the stored deleter. If D is a reference type then get_deleter() returns a reference to the lvalue d.
[ Example:
D d; unique_ptr<int, D> p1(new int, D()); // D must be MoveConstructible unique_ptr<int, D> p2(new int, d); // D must be CopyConstructible unique_ptr<int, D&> p3(new int, d); // p3 holds a reference to d unique_ptr<int, const D&> p4(new int, D()); // error: rvalue deleter object combined // with reference deleter type
— end example ]
unique_ptr(unique_ptr&& u) noexcept;
Requires: If D is not a reference type, D shall satisfy the requirements of MoveConstructible (Table [moveconstructible]). Construction of the deleter from an rvalue of type D shall not throw an exception.
Effects: Constructs a unique_ptr by transferring ownership from u to *this. If D is a reference type, this deleter is copy constructed from u's deleter; otherwise, this deleter is move constructed from u's deleter. [ Note: The deleter constructor can be implemented with std::forward<D>. — end note ]
Postconditions: get() yields the value u.get() yielded before the construction. get_deleter() returns a reference to the stored deleter that was constructed from u.get_deleter(). If D is a reference type then get_deleter() and u.get_deleter() both reference the same lvalue deleter.
template <class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept;
Requires: If E is not a reference type, construction of the deleter from an rvalue of type E shall be well formed and shall not throw an exception. Otherwise, E is a reference type and construction of the deleter from an lvalue of type E shall be well formed and shall not throw an exception.
Remarks: This constructor shall not participate in overload resolution unless:
unique_ptr<U, E>::pointer is implicitly convertible to pointer,
U is not an array type, and
either D is a reference type and E is the same type as D, or D is not a reference type and E is implicitly convertible to D.
Effects: Constructs a unique_ptr by transferring ownership from u to *this. If E is a reference type, this deleter is copy constructed from u's deleter; otherwise, this deleter is move constructed from u's deleter. [ Note: The deleter constructor can be implemented with std::forward<E>. — end note ]
Postconditions: get() yields the value u.get() yielded before the construction. get_deleter() returns a reference to the stored deleter that was constructed from u.get_deleter().
template <class U>
unique_ptr(auto_ptr<U>&& u) noexcept;
Effects: Constructs a unique_ptr object, initializing the stored pointer with u.release() and value-initializing the stored deleter.
Postconditions: get() yields the value u.get() yielded before the construction. u.get() == nullptr. get_deleter() returns a reference to the stored deleter.
Remarks: This constructor shall not participate in overload resolution unless U* is implicitly convertible to T* and D is the same type as default_delete<T>.
20.8.1.2.2 unique_ptr destructor [unique.ptr.single.dtor]
Requires: The expression get_deleter()(get()) shall be well formed, shall have well-defined behavior, and shall not throw exceptions. [ Note: The use of default_delete requires T to be a complete type. — end note ]
Effects: If get() == nullptr there are no effects. Otherwise get_deleter()(get()).
20.8.1.2.3 unique_ptr assignment [unique.ptr.single.asgn]
unique_ptr& operator=(unique_ptr&& u) noexcept;
Requires: If D is not a reference type, D shall satisfy the requirements of MoveAssignable (Table [moveassignable]) and assignment of the deleter from an rvalue of type D shall not throw an exception. Otherwise, D is a reference type; remove_reference_t<D> shall satisfy the CopyAssignable requirements and assignment of the deleter from an lvalue of type D shall not throw an exception.
Effects: Transfers ownership from u to *this as if by calling reset(u.release()) followed by get_deleter() = std::forward<D>(u.get_deleter()).
Returns: *this.
template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
Requires: If E is not a reference type, assignment of the deleter from an rvalue of type E shall be well-formed and shall not throw an exception. Otherwise, E is a reference type and assignment of the deleter from an lvalue of type E shall be well-formed and shall not throw an exception.
Effects: Transfers ownership from u to *this as if by calling reset(u.release()) followed by get_deleter() = std::forward<E>(u.get_deleter()).
Returns: *this.
unique_ptr& operator=(nullptr_t) noexcept;
Effects: reset().
Postcondition: get() == nullptr
Returns: *this.
20.8.1.2.4 unique_ptr observers [unique.ptr.single.observers]
add_lvalue_reference_t<T> operator*() const;
Requires: get() != nullptr.
Returns: *get().
pointer operator->() const noexcept;
Requires: get() != nullptr.
Returns: get().
Note: use typically requires that T be a complete type.
Returns: The stored pointer.
deleter_type& get_deleter() noexcept;
const deleter_type& get_deleter() const noexcept;
Returns: A reference to the stored deleter.
explicit operator bool() const noexcept;
Returns: get() != nullptr.
20.8.1.2.5 unique_ptr modifiers [unique.ptr.single.modifiers]
Postcondition: get() == nullptr.
Returns: The value get() had at the start of the call to release.
void reset(pointer p = pointer()) noexcept;
Requires: The expression get_deleter()(get()) shall be well formed, shall have well-defined behavior, and shall not throw exceptions.
Effects: assigns p to the stored pointer, and then if the old value of the stored pointer, old_p, was not equal to nullptr, calls get_deleter()(old_p). [ Note: The order of these operations is significant because the call to get_deleter() may destroy *this. — end note ]
Postconditions: get() == p. [ Note: The postcondition does not hold if the call to get_deleter() destroys *this since this->get() is no longer a valid expression. — end note ]
void swap(unique_ptr& u) noexcept;
Requires: get_deleter() shall be swappable ([swappable.requirements]) and shall not throw an exception under swap.
Effects: Invokes swap on the stored pointers and on the stored deleters of *this and u.
20.8.1.3 unique_ptr for array objects with a runtime length [unique.ptr.runtime]
namespace std {
template <class T, class D> class unique_ptr<T[], D> {
public:
typedef see below pointer;
typedef T element_type;
typedef D deleter_type;
// [unique.ptr.runtime.ctor], constructors
constexpr unique_ptr() noexcept;
explicit unique_ptr(pointer p) noexcept;
unique_ptr(pointer p, see below d) noexcept;
unique_ptr(pointer p, see below d) noexcept;
unique_ptr(unique_ptr&& u) noexcept;
constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }
// destructor
~unique_ptr();
// assignment
unique_ptr& operator=(unique_ptr&& u) noexcept;
unique_ptr& operator=(nullptr_t) noexcept;
// [unique.ptr.runtime.observers], observers
T& operator[](size_t i) const;
pointer get() const noexcept;
deleter_type& get_deleter() noexcept;
const deleter_type& get_deleter() const noexcept;
explicit operator bool() const noexcept;
// [unique.ptr.runtime.modifiers] modifiers
pointer release() noexcept;
void reset(pointer p = pointer()) noexcept;
void reset(nullptr_t) noexcept;
template <class U> void reset(U) = delete;
void swap(unique_ptr& u) noexcept;
// disable copy from lvalue
unique_ptr(const unique_ptr&) = delete;
unique_ptr& operator=(const unique_ptr&) = delete;
};
}
A specialization for array types is provided with a slightly altered interface.
Conversions between different types of unique_ptr<T[], D> or to or from the non-array forms of unique_ptr produce an ill-formed program.
Pointers to types derived from T are rejected by the constructors, and by reset.
The observers operator* and operator-> are not provided.
The indexing observer operator[] is provided.
The default deleter will call delete[].
Descriptions are provided below only for member functions that have behavior different from the primary template.
The template argument T shall be a complete type.
20.8.1.3.1 unique_ptr constructors [unique.ptr.runtime.ctor]
explicit unique_ptr(pointer p) noexcept;
unique_ptr(pointer p, see below d) noexcept;
unique_ptr(pointer p, see below d) noexcept;
These constructors behave the same as in the primary template except that they do not accept pointer types which are convertible to pointer. [ Note: One implementation technique is to create private templated overloads of these members. — end note ]
20.8.1.3.2 unique_ptr observers [unique.ptr.runtime.observers]
T& operator[](size_t i) const;
Requires: i < the number of elements in the array to which the stored pointer points.
Returns: get()[i].
20.8.1.3.3 unique_ptr modifiers [unique.ptr.runtime.modifiers]
void reset(nullptr_t p) noexcept;
Effects: Equivalent to reset(pointer()).
20.8.1.4 unique_ptr creation [unique.ptr.create]
template <class T, class... Args> unique_ptr<T> make_unique(Args&&... args);
Remarks: This function shall not participate in overload resolution unless T is not an array.
Returns: unique_ptr<T>(new T(std::forward<Args>(args)...)).
template <class T> unique_ptr<T> make_unique(size_t n);
Remarks: This function shall not participate in overload resolution unless T is an array of unknown bound.
Returns: unique_ptr<T>(new remove_extent_t<T>[n]()).
template <class T, class... Args> unspecified make_unique(Args&&...) = delete;
Remarks: This function shall not participate in overload resolution unless T is an array of known bound.
20.8.1.5 unique_ptr specialized algorithms [unique.ptr.special]
template <class T, class D> void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y) noexcept;
Effects: Calls x.swap(y).
template <class T1, class D1, class T2, class D2>
bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
Returns: x.get() == y.get().
template <class T1, class D1, class T2, class D2>
bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
Returns: x.get() != y.get().
template <class T1, class D1, class T2, class D2>
bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
Requires: Let CT be common_type<unique_ptr<T1, D1>::pointer, unique_ptr<T2, D2>::pointer>::type. Then the specialization less<CT> shall be a function object type ([function.objects]) that induces a strict weak ordering ([alg.sorting]) on the pointer values.
Returns: less<CT>()(x.get(), y.get()).
Remarks: If unique_ptr<T1, D1>::pointer is not implicitly convertible to CT or unique_ptr<T2, D2>::pointer is not implicitly convertible to CT, the program is ill-formed.
template <class T1, class D1, class T2, class D2>
bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
Returns: !(y < x).
template <class T1, class D1, class T2, class D2>
bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
Returns: y < x.
template <class T1, class D1, class T2, class D2>
bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
Returns: !(x < y).
template <class T, class D>
bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
template <class T, class D>
bool operator==(nullptr_t, const unique_ptr<T, D>& x) noexcept;
Returns: !x.
template <class T, class D>
bool operator!=(const unique_ptr<T, D>& x, nullptr_t) noexcept;
template <class T, class D>
bool operator!=(nullptr_t, const unique_ptr<T, D>& x) noexcept;
Returns: (bool)x.
template <class T, class D>
bool operator<(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator<(nullptr_t, const unique_ptr<T, D>& x);
Requires: The specialization less<unique_ptr<T, D>::pointer> shall be a function object type ([function.objects]) that induces a strict weak ordering ([alg.sorting]) on the pointer values.
Returns:
The first function template returns
less<unique_ptr<T, D>::pointer>()(x.get(),
nullptr).
The second function template returns
less<unique_ptr<T, D>::pointer>()(nullptr, x.get()).
template <class T, class D>
bool operator>(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator>(nullptr_t, const unique_ptr<T, D>& x);
Returns: The first function template returns nullptr < x. The second function template returns x < nullptr.
template <class T, class D>
bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator<=(nullptr_t, const unique_ptr<T, D>& x);
Returns: The first function template returns !(nullptr < x). The second function template returns !(x < nullptr).
template <class T, class D>
bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
template <class T, class D>
bool operator>=(nullptr_t, const unique_ptr<T, D>& x);
Returns: The first function template returns !(x < nullptr). The second function template returns !(nullptr < x).
20.8.2 Shared-ownership pointers [util.smartptr]
20.8.2.1 Class bad_weak_ptr [util.smartptr.weakptr]
namespace std {
class bad_weak_ptr: public std::exception {
public:
bad_weak_ptr() noexcept;
};
} // namespace std
An exception of type bad_weak_ptr is thrown by the shared_ptr constructor taking a weak_ptr.
Postconditions: what() returns "bad_weak_ptr".
20.8.2.3 Class template weak_ptr [util.smartptr.weak]
The weak_ptr class template stores a weak reference to an object that is already managed by a shared_ptr. To access the object, a weak_ptr can be converted to a shared_ptr using the member function lock.
namespace std {
template<class T> class weak_ptr {
public:
typedef T element_type;
// [util.smartptr.weak.const], constructors
constexpr weak_ptr() noexcept;
template<class Y> weak_ptr(shared_ptr<Y> const& r) noexcept;
weak_ptr(weak_ptr const& r) noexcept;
template<class Y> weak_ptr(weak_ptr<Y> const& r) noexcept;
weak_ptr(weak_ptr&& r) noexcept;
template<class Y> weak_ptr(weak_ptr<Y>&& r) noexcept;
// [util.smartptr.weak.dest], destructor
~weak_ptr();
// [util.smartptr.weak.assign], assignment
weak_ptr& operator=(weak_ptr const& r) noexcept;
template<class Y> weak_ptr& operator=(weak_ptr<Y> const& r) noexcept;
template<class Y> weak_ptr& operator=(shared_ptr<Y> const& r) noexcept;
weak_ptr& operator=(weak_ptr&& r) noexcept;
template<class Y> weak_ptr& operator=(weak_ptr<Y>&& r) noexcept;
// [util.smartptr.weak.mod], modifiers
void swap(weak_ptr& r) noexcept;
void reset() noexcept;
// [util.smartptr.weak.obs], observers
long use_count() const noexcept;
bool expired() const noexcept;
shared_ptr<T> lock() const noexcept;
template<class U> bool owner_before(shared_ptr<U> const& b) const;
template<class U> bool owner_before(weak_ptr<U> const& b) const;
};
// [util.smartptr.weak.spec], specialized algorithms
template<class T> void swap(weak_ptr<T>& a, weak_ptr<T>& b) noexcept;
} // namespace std
Specializations of weak_ptr shall be CopyConstructible and CopyAssignable, allowing their use in standard containers. The template parameter T of weak_ptr may be an incomplete type.
20.8.2.3.1 weak_ptr constructors [util.smartptr.weak.const]
constexpr weak_ptr() noexcept;
Effects: Constructs an empty weak_ptr object.
Postconditions: use_count() == 0.
weak_ptr(const weak_ptr& r) noexcept;
template<class Y> weak_ptr(const weak_ptr<Y>& r) noexcept;
template<class Y> weak_ptr(const shared_ptr<Y>& r) noexcept;
Remark: The second and third constructors shall not participate in overload resolution unless Y* is implicitly convertible to T*.
Effects: If r is empty, constructs an empty weak_ptr object; otherwise, constructs a weak_ptr object that shares ownership with r and stores a copy of the pointer stored in r.
Postconditions: use_count() == r.use_count().
weak_ptr(weak_ptr&& r) noexcept;
template<class Y> weak_ptr(weak_ptr<Y>&& r) noexcept;
Remark: The second constructor shall not participate in overload resolution unless Y* is implicitly convertible to T*.
Effects: Move-constructs a weak_ptr instance from r.
Postconditions: *this shall contain the old value of r. r shall be empty. r.use_count() == 0.
20.8.2.3.2 weak_ptr destructor [util.smartptr.weak.dest]
Effects: Destroys this weak_ptr object but has no effect on the object its stored pointer points to.
20.8.2.3.3 weak_ptr assignment [util.smartptr.weak.assign]
weak_ptr& operator=(const weak_ptr& r) noexcept;
template<class Y> weak_ptr& operator=(const weak_ptr<Y>& r) noexcept;
template<class Y> weak_ptr& operator=(const shared_ptr<Y>& r) noexcept;
Effects: Equivalent to weak_ptr(r).swap(*this).
Remarks: The implementation may meet the effects (and the implied guarantees) via different means, without creating a temporary.
Returns: *this.
weak_ptr& operator=(weak_ptr&& r) noexcept;
template<class Y> weak_ptr& operator=(weak_ptr<Y>&& r) noexcept;
Effects: Equivalent to weak_ptr(std::move(r)).swap(*this).
Returns: *this.
20.8.2.3.4 weak_ptr modifiers [util.smartptr.weak.mod]
void swap(weak_ptr& r) noexcept;
Effects: Exchanges the contents of *this and r.
Effects: Equivalent to weak_ptr().swap(*this).
20.8.2.3.5 weak_ptr observers [util.smartptr.weak.obs]
long use_count() const noexcept;
Returns: 0 if *this is empty; otherwise, the number of shared_ptr instances that share ownership with *this.
[ Note: use_count() is not necessarily efficient. — end note ]
bool expired() const noexcept;
Returns: use_count() == 0.
[ Note: expired() may be faster than use_count(). — end note ]
shared_ptr<T> lock() const noexcept;
Returns: expired() ? shared_ptr<T>() : shared_ptr<T>(*this), executed atomically.
template<class U> bool owner_before(shared_ptr<U> const& b) const;
template<class U> bool owner_before(weak_ptr<U> const& b) const;
Returns: An unspecified value such that
x.owner_before(y) defines a strict weak ordering as defined in [alg.sorting];
under the equivalence relation defined by owner_before, !a.owner_before(b) && !b.owner_before(a), two shared_ptr or weak_ptr instances are equivalent if and only if they share ownership or are both empty.
20.8.2.3.6 weak_ptr specialized algorithms [util.smartptr.weak.spec]
template<class T> void swap(weak_ptr<T>& a, weak_ptr<T>& b) noexcept;
Effects: Equivalent to a.swap(b).
20.8.2.4 Class template owner_less [util.smartptr.ownerless]
The class template owner_less allows ownership-based mixed comparisons of shared and weak pointers.
namespace std {
template<class T> struct owner_less;
template<class T> struct owner_less<shared_ptr<T> > {
typedef bool result_type;
typedef shared_ptr<T> first_argument_type;
typedef shared_ptr<T> second_argument_type;
bool operator()(shared_ptr<T> const&, shared_ptr<T> const&) const;
bool operator()(shared_ptr<T> const&, weak_ptr<T> const&) const;
bool operator()(weak_ptr<T> const&, shared_ptr<T> const&) const;
};
template<class T> struct owner_less<weak_ptr<T> > {
typedef bool result_type;
typedef weak_ptr<T> first_argument_type;
typedef weak_ptr<T> second_argument_type;
bool operator()(weak_ptr<T> const&, weak_ptr<T> const&) const;
bool operator()(shared_ptr<T> const&, weak_ptr<T> const&) const;
bool operator()(weak_ptr<T> const&, shared_ptr<T> const&) const;
};
}
operator()(x,y) shall return x.owner_before(y). [ Note: Note that
operator() defines a strict weak ordering as defined in [alg.sorting];
under the equivalence relation defined by operator(), !operator()(a, b) && !operator()(b, a), two shared_ptr or weak_ptr instances are equivalent if and only if they share ownership or are both empty.
— end note ]
20.8.2.5 Class template enable_shared_from_this [util.smartptr.enab]
A class T can inherit from enable_shared_from_this<T> to inherit the shared_from_this member functions that obtain a shared_ptr instance pointing to *this.
[ Example:
struct X: public enable_shared_from_this<X> {
};
int main() {
shared_ptr<X> p(new X);
shared_ptr<X> q = p->shared_from_this();
assert(p == q);
assert(!(p < q ) && !(q < p)); // p and q share ownership
}
— end example ]
namespace std {
template<class T> class enable_shared_from_this {
protected:
constexpr enable_shared_from_this() noexcept;
enable_shared_from_this(enable_shared_from_this const&) noexcept;
enable_shared_from_this& operator=(enable_shared_from_this const&) noexcept;
~enable_shared_from_this();
public:
shared_ptr<T> shared_from_this();
shared_ptr<T const> shared_from_this() const;
};
} // namespace std
The template parameter T of enable_shared_from_this may be an incomplete type.
constexpr enable_shared_from_this() noexcept;
enable_shared_from_this(const enable_shared_from_this<T>&) noexcept;
Effects: Constructs an enable_shared_from_this<T> object.
enable_shared_from_this<T>& operator=(const enable_shared_from_this<T>&) noexcept;
Returns: *this.
Effects: Destroys *this.
shared_ptr<T> shared_from_this();
shared_ptr<T const> shared_from_this() const;
Requires: enable_shared_from_this<T> shall be an accessible base class of T. *this shall be a subobject of an object t of type T. There shall be at least one shared_ptr instance p that owns &t.
Returns: A shared_ptr<T> object r that shares ownership with p.
Postconditions: r.get() == this.
[ Note: A possible implementation is shown below:
template<class T> class enable_shared_from_this {
private:
weak_ptr<T> __weak_this;
protected:
constexpr enable_shared_from_this() : __weak_this() { }
enable_shared_from_this(enable_shared_from_this const &) { }
enable_shared_from_this& operator=(enable_shared_from_this const &) { return *this; }
~enable_shared_from_this() { }
public:
shared_ptr<T> shared_from_this() { return shared_ptr<T>(__weak_this); }
shared_ptr<T const> shared_from_this() const { return shared_ptr<T const>(__weak_this); }
};
The shared_ptr constructors that create unique pointers can detect the presence of an enable_shared_from_this base and assign the newly created shared_ptr to its __weak_this member. — end note ]
20.8.2.7 Smart pointer hash support [util.smartptr.hash]
template <class T, class D> struct hash<unique_ptr<T, D> >;
The template specialization shall meet the requirements of class template hash ([unord.hash]). For an object p of type UP, where UP is unique_ptr<T, D>, hash<UP>()(p) shall evaluate to the same value as hash<typename UP::pointer>()(p.get()).
Requires: The specialization hash<typename UP::pointer> shall be well-formed and well-defined, and shall meet the requirements of class template hash ([unord.hash]).
template <class T> struct hash<shared_ptr<T> >;
The template specialization shall meet the requirements of class template hash ([unord.hash]). For an object p of type shared_ptr<T>, hash<shared_ptr<T> >()(p) shall evaluate to the same value as hash<T*>()(p.get()).
20.9 Function objects [function.objects]
A function object type is an object type ([basic.types]) that can be the type of the postfix-expression in a function call ([expr.call], [over.match.call]).231 A function object is an object of a function object type. In the places where one would expect to pass a pointer to a function to an algorithmic template (Clause [algorithms]), the interface is specified to accept a function object. This not only makes algorithmic templates work with pointers to functions, but also enables them to work with arbitrary function objects.
Header <functional> synopsis
namespace std {
// [depr.base], base (deprecated):
template <class Arg, class Result> struct unary_function;
template <class Arg1, class Arg2, class Result> struct binary_function;
// [refwrap], reference_wrapper:
template <class T> class reference_wrapper;
template <class T> reference_wrapper<T> ref(T&) noexcept;
template <class T> reference_wrapper<const T> cref(const T&) noexcept;
template <class T> void ref(const T&&) = delete;
template <class T> void cref(const T&&) = delete;
template <class T> reference_wrapper<T> ref(reference_wrapper<T>) noexcept;
template <class T> reference_wrapper<const T> cref(reference_wrapper<T>) noexcept;
// [arithmetic.operations], arithmetic operations:
template <class T = void> struct plus;
template <class T = void> struct minus;
template <class T = void> struct multiplies;
template <class T = void> struct divides;
template <class T = void> struct modulus;
template <class T = void> struct negate;
template <> struct plus<void>;
template <> struct minus<void>;
template <> struct multiplies<void>;
template <> struct divides<void>;
template <> struct modulus<void>;
template <> struct negate<void>;
// [comparisons], comparisons:
template <class T = void> struct equal_to;
template <class T = void> struct not_equal_to;
template <class T = void> struct greater;
template <class T = void> struct less;
template <class T = void> struct greater_equal;
template <class T = void> struct less_equal;
template <> struct equal_to<void>;
template <> struct not_equal_to<void>;
template <> struct greater<void>;
template <> struct less<void>;
template <> struct greater_equal<void>;
template <> struct less_equal<void>;
// [logical.operations], logical operations:
template <class T = void> struct logical_and;
template <class T = void> struct logical_or;
template <class T = void> struct logical_not;
template <> struct logical_and<void>;
template <> struct logical_or<void>;
template <> struct logical_not<void>;
// [bitwise.operations], bitwise operations:
template <class T = void> struct bit_and;
template <class T = void> struct bit_or;
template <class T = void> struct bit_xor;
template <class T = void> struct bit_not;
template <> struct bit_and<void>;
template <> struct bit_or<void>;
template <> struct bit_xor<void>;
template <> struct bit_not<void>;
// [negators], negators:
template <class Predicate> class unary_negate;
template <class Predicate>
constexpr unary_negate<Predicate> not1(const Predicate&);
template <class Predicate> class binary_negate;
template <class Predicate>
constexpr binary_negate<Predicate> not2(const Predicate&);
// [func.bind], bind:
template<class T> struct is_bind_expression;
template<class T> struct is_placeholder;
template<class F, class... BoundArgs>
unspecified bind(F&&, BoundArgs&&...);
template<class R, class F, class... BoundArgs>
unspecified bind(F&&, BoundArgs&&...);
namespace placeholders {
// M is the implementation-defined number of placeholders
extern unspecified _1;
extern unspecified _2;
.
.
.
extern unspecified _M;
}
// [depr.lib.binders], binders (deprecated):
template <class Fn> class binder1st;
template <class Fn, class T>
binder1st<Fn> bind1st(const Fn&, const T&);
template <class Fn> class binder2nd;
template <class Fn, class T>
binder2nd<Fn> bind2nd(const Fn&, const T&);
// [depr.function.pointer.adaptors], adaptors (deprecated):
template <class Arg, class Result> class pointer_to_unary_function;
template <class Arg, class Result>
pointer_to_unary_function<Arg,Result> ptr_fun(Result (*)(Arg));
template <class Arg1, class Arg2, class Result>
class pointer_to_binary_function;
template <class Arg1, class Arg2, class Result>
pointer_to_binary_function<Arg1,Arg2,Result>
ptr_fun(Result (*)(Arg1,Arg2));
// [depr.member.pointer.adaptors], adaptors (deprecated):
template<class S, class T> class mem_fun_t;
template<class S, class T, class A> class mem_fun1_t;
template<class S, class T>
mem_fun_t<S,T> mem_fun(S (T::*f)());
template<class S, class T, class A>
mem_fun1_t<S,T,A> mem_fun(S (T::*f)(A));
template<class S, class T> class mem_fun_ref_t;
template<class S, class T, class A> class mem_fun1_ref_t;
template<class S, class T>
mem_fun_ref_t<S,T> mem_fun_ref(S (T::*f)());
template<class S, class T, class A>
mem_fun1_ref_t<S,T,A> mem_fun_ref(S (T::*f)(A));
template <class S, class T> class const_mem_fun_t;
template <class S, class T, class A> class const_mem_fun1_t;
template <class S, class T>
const_mem_fun_t<S,T> mem_fun(S (T::*f)() const);
template <class S, class T, class A>
const_mem_fun1_t<S,T,A> mem_fun(S (T::*f)(A) const);
template <class S, class T> class const_mem_fun_ref_t;
template <class S, class T, class A> class const_mem_fun1_ref_t;
template <class S, class T>
const_mem_fun_ref_t<S,T> mem_fun_ref(S (T::*f)() const);
template <class S, class T, class A>
const_mem_fun1_ref_t<S,T,A> mem_fun_ref(S (T::*f)(A) const);
// [func.memfn], member function adaptors:
template<class R, class T> unspecified mem_fn(R T::*);
// [func.wrap] polymorphic function wrappers:
class bad_function_call;
template<class> class function; // undefined
template<class R, class... ArgTypes> class function<R(ArgTypes...)>;
template<class R, class... ArgTypes>
void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
template<class R, class... ArgTypes>
bool operator==(const function<R(ArgTypes...)>&, nullptr_t);
template<class R, class... ArgTypes>
bool operator==(nullptr_t, const function<R(ArgTypes...)>&);
template<class R, class... ArgTypes>
bool operator!=(const function<R(ArgTypes...)>&, nullptr_t);
template<class R, class... ArgTypes>
bool operator!=(nullptr_t, const function<R(ArgTypes...)>&);
// [unord.hash], hash function primary template:
template <class T> struct hash;
// Hash function specializations
template <> struct hash<bool>;
template <> struct hash<char>;
template <> struct hash<signed char>;
template <> struct hash<unsigned char>;
template <> struct hash<char16_t>;
template <> struct hash<char32_t>;
template <> struct hash<wchar_t>;
template <> struct hash<short>;
template <> struct hash<unsigned short>;
template <> struct hash<int>;
template <> struct hash<unsigned int>;
template <> struct hash<long>;
template <> struct hash<long long>;
template <> struct hash<unsigned long>;
template <> struct hash<unsigned long long>;
template <> struct hash<float>;
template <> struct hash<double>;
template <> struct hash<long double>;
template<class T> struct hash<T*>;
}
[ Example: If a C++ program wants to have a by-element addition of two vectors a and b containing double and put the result into a, it can do:
transform(a.begin(), a.end(), b.begin(), a.begin(), plus<double>());
— end example ]
[ Example: To negate every element of a:
transform(a.begin(), a.end(), a.begin(), negate<double>());
— end example ]
[ Note: To enable adaptors and other components to manipulate function objects that take one or two arguments many of the function objects in this clause correspondingly provide typedefs argument_type and result_type for function objects that take one argument and first_argument_type, second_argument_type, and result_type for function objects that take two arguments. — end note ]
Such a type is a function pointer or a class type which has a member operator() or a class type which has a conversion to a pointer to function.
20.9.1 Definitions [func.def]
The following definitions apply to this Clause:
A call signature is the name of a return type followed by a parenthesized comma-separated list of zero or more argument types.
A callable type is a function object type ([function.objects]) or a pointer to member.
A callable object is an object of a callable type.
A call wrapper type is a type that holds a callable object and supports a call operation that forwards to that object.
A call wrapper is an object of a call wrapper type.
A target object is the callable object held by a call wrapper.
20.9.2 Requirements [func.require]
Define INVOKE(f, t1, t2, ..., tN) as follows:
(t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T and t1 is an object of type T or a reference to an object of type T or a reference to an object of a type derived from T;
((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a class T and t1 is not one of the types described in the previous item;
t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is an object of type T or a reference to an object of type T or a reference to an object of a type derived from T;
(*t1).*f when N == 1 and f is a pointer to member data of a class T and t1 is not one of the types described in the previous item;
f(t1, t2, ..., tN) in all other cases.
If a call wrapper ([func.def]) has a weak result type the type of its member type result_type is based on the type T of the wrapper's target object ([func.def]):
if T is a pointer to function type, result_type shall be a synonym for the return type of T;
if T is a pointer to member function, result_type shall be a synonym for the return type of T;
if T is a class type with a member type result_type, then result_type shall be a synonym for T::result_type;
otherwise result_type shall not be defined.
Every call wrapper ([func.def]) shall be MoveConstructible. A simple call wrapper is a call wrapper that is CopyConstructible and CopyAssignable and whose copy constructor, move constructor, and assignment operator do not throw exceptions. A forwarding call wrapper is a call wrapper that can be called with an arbitrary argument list and delivers the arguments to the wrapped callable object as references. This forwarding step shall ensure that rvalue arguments are delivered as rvalue-references and lvalue arguments are delivered as lvalue-references. [ Note: In a typical implementation forwarding call wrappers have an overloaded function call operator of the form
template<class... UnBoundArgs> R operator()(UnBoundArgs&&... unbound_args) cv-qual;
— end note ]
20.9.3 Class template reference_wrapper [refwrap]
namespace std {
template <class T> class reference_wrapper {
public :
// types
typedef T type;
typedef see below result_type; // not always defined
typedef see below argument_type; // not always defined
typedef see below first_argument_type; // not always defined
typedef see below second_argument_type; // not always defined
// construct/copy/destroy
reference_wrapper(T&) noexcept;
reference_wrapper(T&&) = delete; // do not bind to temporary objects
reference_wrapper(const reference_wrapper& x) noexcept;
// assignment
reference_wrapper& operator=(const reference_wrapper& x) noexcept;
// access
operator T& () const noexcept;
T& get() const noexcept;
// invocation
template <class... ArgTypes>
result_of_t<T&(ArgTypes&&...)>
operator() (ArgTypes&&...) const;
};
}
reference_wrapper<T> is a CopyConstructible and CopyAssignable wrapper around a reference to an object or function of type T.
reference_wrapper<T> has a weak result type ([func.require]). If T is a function type, result_type shall be a synonym for the return type of T.
The template specialization reference_wrapper<T> shall define a nested type named argument_type as a synonym for T1 only if the type T is any of the following:
a function type or a pointer to function type taking one argument of type T1
a pointer to member function R T0::f cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*
a class type with a member type argument_type; the type T1 is T::argument_type.
The template instantiation reference_wrapper<T> shall define two nested types named first_argument_type and second_argument_type as synonyms for T1 and T2, respectively, only if the type T is any of the following:
a function type or a pointer to function type taking two arguments of types T1 and T2
a pointer to member function R T0::f(T2) cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*
a class type with member types first_argument_type and second_argument_type; the type T1 is T::first_argument_type and the type T2 is T::second_argument_type.
20.9.3.1 reference_wrapper construct/copy/destroy [refwrap.const]
reference_wrapper(T& t) noexcept;
Effects: Constructs a reference_wrapper object that stores a reference to t.
reference_wrapper(const reference_wrapper& x) noexcept;
Effects: Constructs a reference_wrapper object that stores a reference to x.get().
20.9.3.2 reference_wrapper assignment [refwrap.assign]
reference_wrapper& operator=(const reference_wrapper& x) noexcept;
Postconditions: *this stores a reference to x.get().
20.9.3.3 reference_wrapper access [refwrap.access]
operator T& () const noexcept;
Returns: The stored reference.
Returns: The stored reference.
20.9.3.4 reference_wrapper invocation [refwrap.invoke]
template <class... ArgTypes>
result_of_t<T&(ArgTypes&&... )>
operator()(ArgTypes&&... args) const;
Returns: INVOKE(get(), std::forward<ArgTypes>(args)...). ([func.require])
Remark: operator() is described for exposition only. Implementations are not required to provide an actual reference_wrapper::operator(). Implementations are permitted to support reference_wrapper function invocation through multiple overloaded operators or through other means.
20.9.3.5 reference_wrapper helper functions [refwrap.helpers]
template <class T> reference_wrapper<T> ref(T& t) noexcept;
Returns: reference_wrapper<T>(t)
template <class T> reference_wrapper<T> ref(reference_wrapper<T> t) noexcept;
Returns: ref(t.get())
template <class T> reference_wrapper<const T> cref(const T& t) noexcept;
Returns: reference_wrapper <const T>(t)
template <class T> reference_wrapper<const T> cref(reference_wrapper<T> t) noexcept;
Returns: cref(t.get());
20.9.4 Arithmetic operations [arithmetic.operations]
The library provides basic function object classes for all of the arithmetic operators in the language ([expr.mul], [expr.add]).
template <class T = void> struct plus {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x + y.
template <class T = void> struct minus {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x - y.
template <class T = void> struct multiplies {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x * y.
template <class T = void> struct divides {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x / y.
template <class T = void> struct modulus {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x % y.
template <class T = void> struct negate {
constexpr T operator()(const T& x) const;
typedef T argument_type;
typedef T result_type;
};
operator() returns -x.
template <> struct plus<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) + std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) + std::forward<U>(u).
template <> struct minus<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) - std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) - std::forward<U>(u).
template <> struct multiplies<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) * std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) * std::forward<U>(u).
template <> struct divides<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) / std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) / std::forward<U>(u).
template <> struct modulus<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) % std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) % std::forward<U>(u).
template <> struct negate<void> {
template <class T> constexpr auto operator()(T&& t) const
-> decltype(-std::forward<T>(t));
typedef unspecified is_transparent;
};
operator() returns -std::forward<T>(t).
20.9.5 Comparisons [comparisons]
The library provides basic function object classes for all of the comparison operators in the language ([expr.rel], [expr.eq]).
template <class T = void> struct equal_to {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x == y.
template <class T = void> struct not_equal_to {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x != y.
template <class T = void> struct greater {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x > y.
template <class T = void> struct less {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x < y.
template <class T = void> struct greater_equal {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x >= y.
template <class T = void> struct less_equal {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x <= y.
template <> struct equal_to<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) == std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) == std::forward<U>(u).
template <> struct not_equal_to<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) != std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) != std::forward<U>(u).
template <> struct greater<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) > std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) > std::forward<U>(u).
template <> struct less<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) < std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) < std::forward<U>(u).
template <> struct greater_equal<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) >= std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) >= std::forward<U>(u).
template <> struct less_equal<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) <= std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) <= std::forward<U>(u).
For templates greater, less, greater_equal, and less_equal, the specializations for any pointer type yield a total order, even if the built-in operators <, >, <=, >= do not.
20.9.6 Logical operations [logical.operations]
The library provides basic function object classes for all of the logical operators in the language ([expr.log.and], [expr.log.or], [expr.unary.op]).
template <class T = void> struct logical_and {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x && y.
template <class T = void> struct logical_or {
constexpr bool operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef bool result_type;
};
operator() returns x || y.
template <class T = void> struct logical_not {
constexpr bool operator()(const T& x) const;
typedef T argument_type;
typedef bool result_type;
};
operator() returns !x.
template <> struct logical_and<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) && std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) && std::forward<U>(u).
template <> struct logical_or<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) || std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) || std::forward<U>(u).
template <> struct logical_not<void> {
template <class T> constexpr auto operator()(T&& t) const
-> decltype(!std::forward<T>(t));
typedef unspecified is_transparent;
};
operator() returns !std::forward<T>(t).
20.9.7 Bitwise operations [bitwise.operations]
The library provides basic function object classes for all of the bitwise operators in the language ([expr.bit.and], [expr.or], [expr.xor], [expr.unary.op]).
template <class T = void> struct bit_and {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x & y.
template <class T = void> struct bit_or {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x | y.
template <class T = void> struct bit_xor {
constexpr T operator()(const T& x, const T& y) const;
typedef T first_argument_type;
typedef T second_argument_type;
typedef T result_type;
};
operator() returns x ^ y.
template <class T = void> struct bit_not {
constexpr T operator()(const T& x) const;
typedef T argument_type;
typedef T result_type;
};
operator() returns ~x.
template <> struct bit_and<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) & std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) & std::forward<U>(u).
template <> struct bit_or<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) | std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) | std::forward<U>(u).
template <> struct bit_xor<void> {
template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
-> decltype(std::forward<T>(t) ^ std::forward<U>(u));
typedef unspecified is_transparent;
};
operator() returns std::forward<T>(t) ^ std::forward<U>(u).
template <> struct bit_not<void> {
template <class T> constexpr auto operator()(T&& t) const
-> decltype(~std::forward<T>(t));
typedef unspecified is_transparent;
};
operator() returns ~std::forward<T>(t).
20.9.8 Negators [negators]
Negators not1 and not2 take a unary and a binary predicate, respectively, and return their complements ([expr.unary.op]).
template <class Predicate>
class unary_negate {
public:
constexpr explicit unary_negate(const Predicate& pred);
constexpr bool operator()(const typename Predicate::argument_type& x) const;
typedef typename Predicate::argument_type argument_type;
typedef bool result_type;
};
operator() returns !pred(x).
template <class Predicate>
constexpr unary_negate<Predicate> not1(const Predicate& pred);
Returns: unary_negate<Predicate>(pred).
template <class Predicate>
class binary_negate {
public:
constexpr explicit binary_negate(const Predicate& pred);
constexpr bool operator()(const typename Predicate::first_argument_type& x,
const typename Predicate::second_argument_type& y) const;
typedef typename Predicate::first_argument_type first_argument_type;
typedef typename Predicate::second_argument_type second_argument_type;
typedef bool result_type;
};
operator() returns !pred(x,y).
template <class Predicate>
constexpr binary_negate<Predicate> not2(const Predicate& pred);
Returns: binary_negate<Predicate>(pred).
20.9.9 Function object binders [func.bind]
This subclause describes a uniform mechanism for binding arguments of callable objects.
20.9.9.1 Class template is_bind_expression [func.bind.isbind]
namespace std {
template<class T> struct is_bind_expression; // see below
}
is_bind_expression can be used to detect function objects generated by bind. bind uses is_bind_expression to detect subexpressions.
Instantiations of the is_bind_expression template shall meet the UnaryTypeTrait requirements ([meta.rqmts]). The implementation shall provide a definition that has a BaseCharacteristic of true_type if T is a type returned from bind, otherwise it shall have a BaseCharacteristic of false_type. A program may specialize this template for a user-defined type T to have a BaseCharacteristic of true_type to indicate that T should be treated as a subexpression in a bind call.
20.9.9.2 Class template is_placeholder [func.bind.isplace]
namespace std {
template<class T> struct is_placeholder; // see below
}
is_placeholder can be used to detect the standard placeholders _1, _2, and so on. bind uses is_placeholder to detect placeholders.
Instantiations of the is_placeholder template shall meet the UnaryTypeTrait requirements ([meta.rqmts]). The implementation shall provide a definition that has the BaseCharacteristic of integral_constant<int, J> if T is the type of std::placeholders::_J, otherwise it shall have a BaseCharacteristic of integral_constant<int, 0>. A program may specialize this template for a user-defined type T to have a BaseCharacteristic of integral_constant<int, N> with N > 0 to indicate that T should be treated as a placeholder type.
20.9.9.3 Function template bind [func.bind.bind]
In the text that follows, the following names have the following meanings:
FD is the type decay_t<F>,
fd is an lvalue of type FD constructed from std::forward<F>(f),
Ti is the ith type in the template parameter pack BoundArgs,
TiD is the type decay_t<Ti>,
ti is the ith argument in the function parameter pack bound_args,
tid is an lvalue of type TiD constructed from std::forward<Ti>(ti),
Uj is the jth deduced type of the UnBoundArgs&&... parameter of the forwarding call wrapper, and
uj is the jth argument associated with Uj.
template<class F, class... BoundArgs>
unspecified bind(F&& f, BoundArgs&&... bound_args);
Requires: is_constructible<FD, F>::value shall be true. For each Ti in BoundArgs, is_constructible<TiD, Ti>::value shall be true. INVOKE (fd, w1, w2, ..., wN) ([func.require]) shall be a valid expression for some values w1, w2, ..., wN, where N == sizeof...(bound_args).
Returns: A forwarding call wrapper g with a weak result type ([func.require]). The effect of g(u1, u2, ..., uM) shall be INVOKE(fd, std::forward<V1>(v1), std::forward<V2>(v2), ..., std::forward<VN>(vN), result_of_t<FD cv & (V1, V2, ..., VN)>), where cv represents the cv-qualifiers of g and the values and types of the bound arguments v1, v2, ..., vN are determined as specified below. The copy constructor and move constructor of the forwarding call wrapper shall throw an exception if and only if the corresponding constructor of FD or of any of the types TiD throws an exception.
Throws: Nothing unless the construction of fd or of one of the values tid throws an exception.
Remarks: The return type shall satisfy the requirements of MoveConstructible. If all of FD and TiD satisfy the requirements of CopyConstructible, then the return type shall satisfy the requirements of CopyConstructible. [ Note: This implies that all of FD and TiD are MoveConstructible. — end note ]
template<class R, class F, class... BoundArgs>
unspecified bind(F&& f, BoundArgs&&... bound_args);
Requires: is_constructible<FD, F>::value shall be true. For each Ti in BoundArgs, is_constructible<TiD, Ti>::value shall be true. INVOKE(fd, w1, w2, ..., wN) shall be a valid expression for some values w1, w2, ..., wN, where N == sizeof...(bound_args).
Returns: A forwarding call wrapper g with a nested type result_type defined as a synonym for R. The effect of g(u1, u2, ..., uM) shall be INVOKE(fd, std::forward<V1>(v1), std::forward<V2>(v2), ..., std::forward<VN>(vN), R), where the values and types of the bound arguments v1, v2, ..., vN are determined as specified below. The copy constructor and move constructor of the forwarding call wrapper shall throw an exception if and only if the corresponding constructor of FD or of any of the types TiD throws an exception.
Throws: Nothing unless the construction of fd or of one of the values tid throws an exception.
Remarks: The return type shall satisfy the requirements of MoveConstructible. If all of FD and TiD satisfy the requirements of CopyConstructible, then the return type shall satisfy the requirements of CopyConstructible. [ Note: This implies that all of FD and TiD are MoveConstructible. — end note ]
The values of the bound arguments v1, v2, ..., vN and their corresponding types V1, V2, ..., VN depend on the types TiD derived from the call to bind and the cv-qualifiers cv of the call wrapper g as follows:
if TiD is reference_wrapper<T>, the argument is tid.get() and its type Vi is T&;
if the value of is_bind_expression<TiD>::value is true, the argument is tid(std::forward<Uj>(uj)...) and its type Vi is result_of_t<TiD cv & (Uj&&...)>&&;
if the value j of is_placeholder<TiD>::value is not zero, the argument is std::forward<Uj>(uj) and its type Vi is Uj&&;
otherwise, the value is tid and its type Vi is TiD cv &.
20.9.9.4 Placeholders [func.bind.place]
namespace std {
namespace placeholders {
// M is the implementation-defined number of placeholders
extern unspecified _1;
extern unspecified _2;
.
.
.
extern unspecified _M;
}
}
All placeholder types shall be DefaultConstructible and CopyConstructible, and their default constructors and copy/move constructors shall not throw exceptions. It is implementation-defined whether placeholder types are CopyAssignable. CopyAssignable placeholders' copy assignment operators shall not throw exceptions.
20.9.10 Function template mem_fn [func.memfn]
template<class R, class T> unspecified mem_fn(R T::* pm);
Returns: A simple call wrapper ([func.def]) fn such that the expression fn(t, a2, ..., aN) is equivalent to INVOKE(pm, t, a2, ..., aN) ([func.require]). fn shall have a nested type result_type that is a synonym for the return type of pm when pm is a pointer to member function.
The simple call wrapper shall define two nested types named argument_type and result_type as synonyms for cv T* and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking no arguments, where Ret is pm's return type.
The simple call wrapper shall define three nested types named first_argument_type, second_argument_type, and result_type as synonyms for cv T*, T1, and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking one argument of type T1, where Ret is pm's return type.
Throws: Nothing.
20.9.11 Polymorphic function wrappers [func.wrap]
This subclause describes a polymorphic wrapper class that encapsulates arbitrary callable objects.
20.9.11.1 Class bad_function_call [func.wrap.badcall]
An exception of type bad_function_call is thrown by function::operator() ([func.wrap.func.inv]) when the function wrapper object has no target.
namespace std {
class bad_function_call : public std::exception {
public:
// [func.wrap.badcall.const], constructor:
bad_function_call() noexcept;
};
} // namespace std
20.9.11.1.1 bad_function_call constructor [func.wrap.badcall.const]
Effects: constructs a bad_function_call object.
20.9.11.2 Class template function [func.wrap.func]
namespace std {
template<class> class function; // undefined
template<class R, class... ArgTypes>
class function<R(ArgTypes...)> {
public:
typedef R result_type;
typedef T1 argument_type; // only if sizeof...(ArgTypes) == 1 and
// the type in ArgTypes is T1
typedef T1 first_argument_type; // only if sizeof...(ArgTypes) == 2 and
// ArgTypes contains T1 and T2
typedef T2 second_argument_type; // only if sizeof...(ArgTypes) == 2 and
// ArgTypes contains T1 and T2
// [func.wrap.func.con], construct/copy/destroy:
function() noexcept;
function(nullptr_t) noexcept;
function(const function&);
function(function&&);
template<class F> function(F);
template<class A> function(allocator_arg_t, const A&) noexcept;
template<class A> function(allocator_arg_t, const A&,
nullptr_t) noexcept;
template<class A> function(allocator_arg_t, const A&,
const function&);
template<class A> function(allocator_arg_t, const A&,
function&&);
template<class F, class A> function(allocator_arg_t, const A&, F);
function& operator=(const function&);
function& operator=(function&&);
function& operator=(nullptr_t);
template<class F> function& operator=(F&&);
template<class F> function& operator=(reference_wrapper<F>) noexcept;
~function();
// [func.wrap.func.mod], function modifiers:
void swap(function&) noexcept;
template<class F, class A> void assign(F&&, const A&);
// [func.wrap.func.cap], function capacity:
explicit operator bool() const noexcept;
// [func.wrap.func.inv], function invocation:
R operator()(ArgTypes...) const;
// [func.wrap.func.targ], function target access:
const std::type_info& target_type() const noexcept;
template<class T> T* target() noexcept;
template<class T> const T* target() const noexcept;
};
// [func.wrap.func.nullptr], Null pointer comparisons:
template <class R, class... ArgTypes>
bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
template <class R, class... ArgTypes>
bool operator==(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
template <class R, class... ArgTypes>
bool operator!=(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
template <class R, class... ArgTypes>
bool operator!=(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
// [func.wrap.func.alg], specialized algorithms:
template <class R, class... ArgTypes>
void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
template<class R, class... ArgTypes, class Alloc>
struct uses_allocator<function<R(ArgTypes...)>, Alloc>
: true_type { };
}
The function class template provides polymorphic wrappers that generalize the notion of a function pointer. Wrappers can store, copy, and call arbitrary callable objects ([func.def]), given a call signature ([func.def]), allowing functions to be first-class objects.
A callable object f of type F is Callable for argument types ArgTypes and return type R if the expression INVOKE(f, declval<ArgTypes>()..., R), considered as an unevaluated operand (Clause [expr]), is well formed ([func.require]).
The function class template is a call wrapper ([func.def]) whose call signature ([func.def]) is R(ArgTypes...).
20.9.11.2.1 function construct/copy/destroy [func.wrap.func.con]
When any function constructor that takes a first argument of type allocator_arg_t is invoked, the second argument shall have a type that conforms to the requirements for Allocator (Table [allocator.requirements]). A copy of the allocator argument is used to allocate memory, if necessary, for the internal data structures of the constructed function object.
function() noexcept;
template <class A> function(allocator_arg_t, const A& a) noexcept;
Postconditions: !*this.
function(nullptr_t) noexcept;
template <class A> function(allocator_arg_t, const A& a, nullptr_t) noexcept;
Postconditions: !*this.
function(const function& f);
template <class A> function(allocator_arg_t, const A& a, const function& f);
Postconditions: !*this if !f; otherwise, *this targets a copy of f.target().
Throws: shall not throw exceptions if f's target is a callable object passed via reference_wrapper or a function pointer. Otherwise, may throw bad_alloc or any exception thrown by the copy constructor of the stored callable object. [ Note: Implementations are encouraged to avoid the use of dynamically allocated memory for small callable objects, for example, where f's target is an object holding only a pointer or reference to an object and a member function pointer. — end note ]
function(function&& f);
template <class A> function(allocator_arg_t, const A& a, function&& f);
Effects: If !f, *this has no target; otherwise, move-constructs the target of f into the target of *this, leaving f in a valid state with an unspecified value.
template<class F> function(F f);
template <class F, class A> function(allocator_arg_t, const A& a, F f);
Requires: F shall be CopyConstructible.
Remarks: These constructors shall not participate in overload resolution unless f is Callable ([func.wrap.func]) for argument types ArgTypes... and return type R.
Otherwise, *this targets a copy of f initialized with std::move(f). [ Note: Implementations are encouraged to avoid the use of dynamically allocated memory for small callable objects, for example, where f's target is an object holding only a pointer or reference to an object and a member function pointer. — end note ]
Throws: shall not throw exceptions when f is a function pointer or a reference_wrapper<T> for some T. Otherwise, may throw bad_alloc or any exception thrown by F's copy or move constructor.
function& operator=(const function& f);
Effects: function(f).swap(*this);
Returns: *this
function& operator=(function&& f);
Effects: Replaces the target of *this with the target of f.
Returns: *this
function& operator=(nullptr_t);
Effects: If *this != nullptr, destroys the target of this.
Postconditions: !(*this).
Returns: *this
template<class F> function& operator=(F&& f);
Effects: function(std::forward<F>(f)).swap(*this);
Returns: *this
Remarks: This assignment operator shall not participate in overload resolution unless declval<typename decay<F>::type&>() is Callable ([func.wrap.func]) for argument types ArgTypes... and return type R.
template<class F> function& operator=(reference_wrapper<F> f) noexcept;
Effects: function(f).swap(*this);
Returns: *this
Effects: If *this != nullptr, destroys the target of this.
20.9.11.2.2 function modifiers [func.wrap.func.mod]
void swap(function& other) noexcept;
Effects: interchanges the targets of *this and other.
template<class F, class A>
void assign(F&& f, const A& a);
Effects: function(allocator_arg, a, std::forward<F>(f)).swap(*this)
20.9.11.2.3 function capacity [func.wrap.func.cap]
explicit operator bool() const noexcept;
Returns: true if *this has a target, otherwise false.
20.9.11.2.4 function invocation [func.wrap.func.inv]
R operator()(ArgTypes... args) const
Effects: INVOKE(f, std::forward<ArgTypes>(args)..., R) ([func.require]), where f is the target object ([func.def]) of *this.
Returns: Nothing if R is void, otherwise the return value of INVOKE(f, std::forward<ArgTypes>(args)..., R).
Throws: bad_function_call if !*this; otherwise, any exception thrown by the wrapped callable object.
20.9.11.2.5 function target access [func.wrap.func.targ]
const std::type_info& target_type() const noexcept;
Returns: If *this has a target of type T, typeid(T); otherwise, typeid(void).
template<class T> T* target() noexcept;
template<class T> const T* target() const noexcept;
Requires: T shall be a type that is Callable ([func.wrap.func]) for parameter types ArgTypes and return type R.
Returns: If target_type() == typeid(T) a pointer to the stored function target; otherwise a null pointer.
20.9.11.2.6 null pointer comparison operators [func.wrap.func.nullptr]
template <class R, class... ArgTypes>
bool operator==(const function<R(ArgTypes...)>& f, nullptr_t) noexcept;
template <class R, class... ArgTypes>
bool operator==(nullptr_t, const function<R(ArgTypes...)>& f) noexcept;
Returns: !f.
template <class R, class... ArgTypes>
bool operator!=(const function<R(ArgTypes...)>& f, nullptr_t) noexcept;
template <class R, class... ArgTypes>
bool operator!=(nullptr_t, const function<R(ArgTypes...)>& f) noexcept;
Returns: (bool) f.
20.9.11.2.7 specialized algorithms [func.wrap.func.alg]
template<class R, class... ArgTypes>
void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>& f2);
Effects: f1.swap(f2);
20.9.12 Class template hash [unord.hash]
The unordered associative containers defined in [unord] use specializations of the class template hash as the default hash function. For all object types Key for which there exists a specialization hash<Key>, and for all enumeration types ([dcl.enum]) Key, the instantiation hash<Key> shall:
satisfy the Hash requirements ([hash.requirements]), with Key as the function call argument type, the DefaultConstructible requirements (Table [defaultconstructible]), the CopyAssignable requirements (Table [copyassignable]),
be swappable ([swappable.requirements]) for lvalues,
provide two nested types result_type and argument_type which shall be synonyms for size_t and Key, respectively,
satisfy the requirement that if k1 == k2 is true, h(k1) == h(k2) is also true, where h is an object of type hash<Key> and k1 and k2 are objects of type Key;
satisfy the requirement that the expression h(k), where h is an object of type hash<Key> and k is an object of type Key, shall not throw an exception unless hash<Key> is a user-defined specialization that depends on at least one user-defined type.
template <> struct hash<bool>;
template <> struct hash<char>;
template <> struct hash<signed char>;
template <> struct hash<unsigned char>;
template <> struct hash<char16_t>;
template <> struct hash<char32_t>;
template <> struct hash<wchar_t>;
template <> struct hash<short>;
template <> struct hash<unsigned short>;
template <> struct hash<int>;
template <> struct hash<unsigned int>;
template <> struct hash<long>;
template <> struct hash<unsigned long>;
template <> struct hash<long long>;
template <> struct hash<unsigned long long>;
template <> struct hash<float>;
template <> struct hash<double>;
template <> struct hash<long double>;
template <class T> struct hash<T*>;
The template specializations shall meet the requirements of class template hash ([unord.hash]).
20.10 Metaprogramming and type traits [meta]
This subclause describes components used by C++ programs, particularly in templates, to support the widest possible range of types, optimise template code usage, detect type related user errors, and perform type inference and transformation at compile time. It includes type classification traits, type property inspection traits, and type transformations. The type classification traits describe a complete taxonomy of all possible C++ types, and state where in that taxonomy a given type belongs. The type property inspection traits allow important characteristics of types or of combinations of types to be inspected. The type transformations allow certain properties of types to be manipulated.
20.10.1 Requirements [meta.rqmts]
A UnaryTypeTrait describes a property of a type. It shall be a class template that takes one template type argument and, optionally, additional arguments that help define the property being described. It shall be DefaultConstructible, CopyConstructible, and publicly and unambiguously derived, directly or indirectly, from its BaseCharacteristic, which is a specialization of the template integral_constant ([meta.help]), with the arguments to the template integral_constant determined by the requirements for the particular property being described. The member names of the BaseCharacteristic shall not be hidden and shall be unambiguously available in the UnaryTypeTrait.
A BinaryTypeTrait describes a relationship between two types. It shall be a class template that takes two template type arguments and, optionally, additional arguments that help define the relationship being described. It shall be DefaultConstructible, CopyConstructible, and publicly and unambiguously derived, directly or indirectly, from its BaseCharacteristic, which is a specialization of the template integral_constant ([meta.help]), with the arguments to the template integral_constant determined by the requirements for the particular relationship being described. The member names of the BaseCharacteristic shall not be hidden and shall be unambiguously available in the BinaryTypeTrait.
A TransformationTrait modifies a property of a type. It shall be a class template that takes one template type argument and, optionally, additional arguments that help define the modification. It shall define a publicly accessible nested type named type, which shall be a synonym for the modified type.
20.10.2 Header <type_traits> synopsis [meta.type.synop]
namespace std {
// [meta.help], helper class:
template <class T, T v> struct integral_constant;
typedef integral_constant<bool, true> true_type;
typedef integral_constant<bool, false> false_type;
// [meta.unary.cat], primary type categories:
template <class T> struct is_void;
template <class T> struct is_null_pointer;
template <class T> struct is_integral;
template <class T> struct is_floating_point;
template <class T> struct is_array;
template <class T> struct is_pointer;
template <class T> struct is_lvalue_reference;
template <class T> struct is_rvalue_reference;
template <class T> struct is_member_object_pointer;
template <class T> struct is_member_function_pointer;
template <class T> struct is_enum;
template <class T> struct is_union;
template <class T> struct is_class;
template <class T> struct is_function;
// [meta.unary.comp], composite type categories:
template <class T> struct is_reference;
template <class T> struct is_arithmetic;
template <class T> struct is_fundamental;
template <class T> struct is_object;
template <class T> struct is_scalar;
template <class T> struct is_compound;
template <class T> struct is_member_pointer;
// [meta.unary.prop], type properties:
template <class T> struct is_const;
template <class T> struct is_volatile;
template <class T> struct is_trivial;
template <class T> struct is_trivially_copyable;
template <class T> struct is_standard_layout;
template <class T> struct is_pod;
template <class T> struct is_literal_type;
template <class T> struct is_empty;
template <class T> struct is_polymorphic;
template <class T> struct is_abstract;
template <class T> struct is_final;
template <class T> struct is_signed;
template <class T> struct is_unsigned;
template <class T, class... Args> struct is_constructible;
template <class T> struct is_default_constructible;
template <class T> struct is_copy_constructible;
template <class T> struct is_move_constructible;
template <class T, class U> struct is_assignable;
template <class T> struct is_copy_assignable;
template <class T> struct is_move_assignable;
template <class T> struct is_destructible;
template <class T, class... Args> struct is_trivially_constructible;
template <class T> struct is_trivially_default_constructible;
template <class T> struct is_trivially_copy_constructible;
template <class T> struct is_trivially_move_constructible;
template <class T, class U> struct is_trivially_assignable;
template <class T> struct is_trivially_copy_assignable;
template <class T> struct is_trivially_move_assignable;
template <class T> struct is_trivially_destructible;
template <class T, class... Args> struct is_nothrow_constructible;
template <class T> struct is_nothrow_default_constructible;
template <class T> struct is_nothrow_copy_constructible;
template <class T> struct is_nothrow_move_constructible;
template <class T, class U> struct is_nothrow_assignable;
template <class T> struct is_nothrow_copy_assignable;
template <class T> struct is_nothrow_move_assignable;
template <class T> struct is_nothrow_destructible;
template <class T> struct has_virtual_destructor;
// [meta.unary.prop.query], type property queries:
template <class T> struct alignment_of;
template <class T> struct rank;
template <class T, unsigned I = 0> struct extent;
// [meta.rel], type relations:
template <class T, class U> struct is_same;
template <class Base, class Derived> struct is_base_of;
template <class From, class To> struct is_convertible;
// [meta.trans.cv], const-volatile modifications:
template <class T> struct remove_const;
template <class T> struct remove_volatile;
template <class T> struct remove_cv;
template <class T> struct add_const;
template <class T> struct add_volatile;
template <class T> struct add_cv;
template <class T>
using remove_const_t = typename remove_const<T>::type;
template <class T>
using remove_volatile_t = typename remove_volatile<T>::type;
template <class T>
using remove_cv_t = typename remove_cv<T>::type;
template <class T>
using add_const_t = typename add_const<T>::type;
template <class T>
using add_volatile_t = typename add_volatile<T>::type;
template <class T>
using add_cv_t = typename add_cv<T>::type;
// [meta.trans.ref], reference modifications:
template <class T> struct remove_reference;
template <class T> struct add_lvalue_reference;
template <class T> struct add_rvalue_reference;
template <class T>
using remove_reference_t = typename remove_reference<T>::type;
template <class T>
using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;
template <class T>
using add_rvalue_reference_t = typename add_rvalue_reference<T>::type;
// [meta.trans.sign], sign modifications:
template <class T> struct make_signed;
template <class T> struct make_unsigned;
template <class T>
using make_signed_t = typename make_signed<T>::type;
template <class T>
using make_unsigned_t = typename make_unsigned<T>::type;
// [meta.trans.arr], array modifications:
template <class T> struct remove_extent;
template <class T> struct remove_all_extents;
template <class T>
using remove_extent_t = typename remove_extent<T>::type;
template <class T>
using remove_all_extents_t = typename remove_all_extents<T>::type;
// [meta.trans.ptr], pointer modifications:
template <class T> struct remove_pointer;
template <class T> struct add_pointer;
template <class T>
using remove_pointer_t = typename remove_pointer<T>::type;
template <class T>
using add_pointer_t = typename add_pointer<T>::type;
// [meta.trans.other], other transformations:
template <std::size_t Len,
std::size_t Align = default-alignment> // see [meta.trans.other]
struct aligned_storage;
template <std::size_t Len, class... Types> struct aligned_union;
template <class T> struct decay;
template <bool, class T = void> struct enable_if;
template <bool, class T, class F> struct conditional;
template <class... T> struct common_type;
template <class T> struct underlying_type;
template <class> class result_of; // not defined
template <class F, class... ArgTypes> class result_of<F(ArgTypes...)>;
template <std::size_t Len,
std::size_t Align = default-alignment > // see [meta.trans.other]
using aligned_storage_t = typename aligned_storage<Len,Align>::type;
template <std::size_t Len, class... Types>
using aligned_union_t = typename aligned_union<Len,Types...>::type;
template <class T>
using decay_t = typename decay<T>::type;
template <bool b, class T = void>
using enable_if_t = typename enable_if<b,T>::type;
template <bool b, class T, class F>
using conditional_t = typename conditional<b,T,F>::type;
template <class... T>
using common_type_t = typename common_type<T...>::type;
template <class T>
using underlying_type_t = typename underlying_type<T>::type;
template <class T>
using result_of_t = typename result_of<T>::type;
} // namespace std
The behavior of a program that adds specializations for any of the class templates defined in this subclause is undefined unless otherwise specified.
20.10.3 Helper classes [meta.help]
namespace std {
template <class T, T v>
struct integral_constant {
static constexpr T value = v;
typedef T value_type;
typedef integral_constant<T,v> type;
constexpr operator value_type() const noexcept { return value; }
constexpr value_type operator()() const noexcept { return value; }
};
typedef integral_constant<bool, true> true_type;
typedef integral_constant<bool, false> false_type;
}
The class template integral_constant and its associated typedefs true_type and false_type are used as base classes to define the interface for various type traits.
20.10.4 Unary type traits [meta.unary]
This sub-clause contains templates that may be used to query the properties of a type at compile time.
Each of these templates shall be a UnaryTypeTrait ([meta.rqmts]) with a BaseCharacteristic of true_type if the corresponding condition is true, otherwise false_type.
20.10.4.1 Primary type categories [meta.unary.cat]
The primary type categories correspond to the descriptions given in section [basic.types] of the C++ standard.
For any given type T, the result of applying one of these templates to T and to cv-qualified T shall yield the same result.
[ Note: For any given type T, exactly one of the primary type categories has a value member that evaluates to true. — end note ]
| Template | Condition | Comments |
|
template <class T> struct is_void; | T is void | |
|
template <class T> struct is_null_pointer; | T is std::nullptr_t ([basic.fundamental]) | |
|
template <class T> struct is_integral; | T is an integral type ([basic.fundamental]) | |
|
template <class T> struct is_floating_point; | T is a floating point type ([basic.fundamental]) | |
|
template <class T> struct is_array; | T is an array type ([basic.compound]) of known or unknown extent | Class template array ([array]) is not an array type. |
|
template <class T> struct is_pointer; | T is a pointer type ([basic.compound]) | Includes pointers to functions but not pointers to non-static members. |
|
template <class T> struct is_lvalue_reference; | T is an lvalue reference type ([dcl.ref]) | |
|
template <class T> struct is_rvalue_reference; | T is an rvalue reference type ([dcl.ref]) | |
|
template <class T> struct is_member_object_pointer; | T is a pointer to non-static data member | |
|
template <class T> struct is_member_function_pointer; | T is a pointer to non-static member function | |
|
template <class T> struct is_enum; | T is an enumeration type ([basic.compound]) | |
|
template <class T> struct is_union; | T is a union type ([basic.compound]) | |
|
template <class T> struct is_class; | T is a class type but not a union type ([basic.compound]) | |
|
template <class T> struct is_function; | T is a function type ([basic.compound]) |
20.10.4.2 Composite type traits [meta.unary.comp]
These templates provide convenient compositions of the primary type categories, corresponding to the descriptions given in section [basic.types].
For any given type T, the result of applying one of these templates to T, and to cv-qualified T shall yield the same result.
| Template | Condition | Comments |
|
template <class T> struct is_reference; | T is an lvalue reference or an rvalue reference | |
|
template <class T> struct is_arithmetic; | T is an arithmetic type ([basic.fundamental]) | |
|
template <class T> struct is_fundamental; | T is a fundamental type ([basic.fundamental]) | |
|
template <class T> struct is_object; | T is an object type ([basic.types]) | |
|
template <class T> struct is_scalar; | T is a scalar type ([basic.types]) | |
|
template <class T> struct is_compound; | T is a compound type ([basic.compound]) | |
|
template <class T> struct is_member_pointer; | T is a pointer to non-static data member or non-static member function |
20.10.4.3 Type properties [meta.unary.prop]
These templates provide access to some of the more important properties of types.
It is unspecified whether the library defines any full or partial specializations of any of these templates.
For all of the class templates X declared in this Clause, instantiating that template with a template-argument that is a class template specialization may result in the implicit instantiation of the template argument if and only if the semantics of X require that the argument must be a complete type.
| Template | Condition | Preconditions |
|
template <class T> struct is_const; | T is const-qualified ([basic.type.qualifier]) | |
| template <class T> struct is_volatile; | T is volatile-qualified ([basic.type.qualifier]) | |
|
template <class T> struct is_trivial; | T is a trivial type ([basic.types]) | remove_all_extents_t<T> shall be a complete type or (possibly cv-qualified) void. |
| template <class T> struct is_trivially_copyable; | T is a trivially copyable type ([basic.types]) | remove_all_extents_t<T> shall be a complete type or (possibly cv-qualified) void. |
| template <class T> struct is_standard_layout; | T is a standard-layout type ([basic.types]) | remove_all_extents_t<T> shall be a complete type or (possibly cv-qualified) void. |
| template <class T> struct is_pod; | T is a POD type ([basic.types]) | remove_all_extents_t<T> shall be a complete type or (possibly cv-qualified) void. |
| template <class T> struct is_literal_type; | T is a literal type ([basic.types]) | remove_all_extents_t<T> shall be a complete type or (possibly cv-qualified) void. |
| template <class T> struct is_empty; | T is a class type, but not a union type, with no non-static data members other than bit-fields of length 0, no virtual member functions, no virtual base classes, and no base class B for which is_empty<B>::value is false. | If T is a non-union class type, T shall be a complete type. |
| template <class T> struct is_polymorphic; | T is a polymorphic class ([class.virtual]) | If T is a non-union class type, T shall be a complete type. |
| template <class T> struct is_abstract; | T is an abstract class ([class.abstract]) | If T is a non-union class type, T shall be a complete type. |
| template <class T> struct is_final; | T is a class type marked with the class-virt-specifier final (Clause [class]). [ Note: A union is a class type that can be marked with final. — end note ] | If T is a class type, T shall be a complete type. |
| template <class T> struct is_signed; | If is_arithmetic<T>::value is true, the same result as integral_constant<bool, T(-1) < T(0)>::value; otherwise, false | |
| template <class T> struct is_unsigned; | If is_arithmetic<T>::value is true, the same result as integral_constant<bool, T(0) < T(-1)>::value; otherwise, false | |
| template <class T, class... Args> struct is_constructible; | see below | T and all types in the parameter pack Args shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. |
| template <class T> struct is_default_constructible; | is_constructible<T>::value is true. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_copy_constructible; | For a referenceable type T, the same result as is_constructible<T, const T&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_move_constructible; | For a referenceable type T, the same result as is_constructible<T, T&&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T, class U> struct is_assignable; | The expression declval<T>() = declval<U>() is well-formed when treated as an unevaluated operand (Clause [expr]). Access checking is performed as if in a context unrelated to T and U. Only the validity of the immediate context of the assignment expression is considered. [ Note: The compilation of the expression can result in side effects such as the instantiation of class template specializations and function template specializations, the generation of implicitly-defined functions, and so on. Such side effects are not in the “immediate context” and can result in the program being ill-formed. — end note ] | T and U shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. |
| template <class T> struct is_copy_assignable; | For a referenceable type T, the same result as is_assignable<T&, const T&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_move_assignable; | For a referenceable type T, the same result as is_assignable<T&, T&&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_destructible; |
For reference types, is_destructible<T>::value is true. For incomplete types and function types, is_destructible<T>::value is false. For object types and given U equal to remove_all_extents_t<T>, if the expression std::declval<U&>().~U() is well-formed when treated as an unevaluated operand (Clause [expr]), then is_destructible<T>::value is true, otherwise it is false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T, class... Args> struct is_trivially_constructible; |
is_constructible<T, Args...>::value is true and the variable definition for is_constructible, as defined below, is known to call no operation that is not trivial ( [basic.types], [special]). | T and all types in the parameter pack Args shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. |
| template <class T> struct is_trivially_default_constructible; | is_trivially_constructible<T>::value is true. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_trivially_copy_constructible; | For a referenceable type T, the same result as is_trivially_constructible<T, const T&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_trivially_move_constructible; | For a referenceable type T, the same result as is_trivially_constructible<T, T&&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T, class U> struct is_trivially_assignable; | is_assignable<T, U>::value is true and the assignment, as defined by is_assignable, is known to call no operation that is not trivial ([basic.types], [special]). | T and U shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. |
| template <class T> struct is_trivially_copy_assignable; | For a referenceable type T, the same result as is_trivially_assignable<T&, const T&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_trivially_move_assignable; | For a referenceable type T, the same result as is_trivially_assignable<T&, T&&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_trivially_destructible; | is_destructible<T>::value is true and the indicated destructor is known to be trivial. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T, class... Args> struct is_nothrow_constructible; | is_constructible<T, Args...>::value is true and the variable definition for is_constructible, as defined below, is known not to throw any exceptions ([expr.unary.noexcept]). | T and all types in the parameter pack Args shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. |
| template <class T> struct is_nothrow_default_constructible; | is_nothrow_constructible<T>::value is true. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_nothrow_copy_constructible; | For a referenceable type T, the same result as is_nothrow_constructible<T, const T&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_nothrow_move_constructible; | For a referenceable type T, the same result as is_nothrow_constructible<T, T&&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T, class U> struct is_nothrow_assignable; | is_assignable<T, U>::value is true and the assignment is known not to throw any exceptions ([expr.unary.noexcept]). | T and U shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. |
| template <class T> struct is_nothrow_copy_assignable; | For a referenceable type T, the same result as is_nothrow_assignable<T&, const T&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_nothrow_move_assignable; | For a referenceable type T, the same result as is_nothrow_assignable<T&, T&&>::value, otherwise false. | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct is_nothrow_destructible; | is_destructible<T>::value is true and the indicated destructor is known not to throw any exceptions ([expr.unary.noexcept]). | T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. |
| template <class T> struct has_virtual_destructor; | T has a virtual destructor ([class.dtor]) | If T is a non-union class type, T shall be a complete type. |
[ Example:
is_const<const volatile int>::value // true is_const<const int*>::value // false is_const<const int&>::value // false is_const<int[3]>::value // false is_const<const int[3]>::value // true
— end example ]
[ Example:
remove_const_t<const volatile int> // volatile int remove_const_t<const int* const> // const int* remove_const_t<const int&> // const int& remove_const_t<const int[3]> // int[3]
— end example ]
[ Example:
// Given: struct P final { }; union U1 { }; union U2 final { }; // the following assertions hold: static_assert(!is_final<int>::value, "Error!"); static_assert( is_final<P>::value, "Error!"); static_assert(!is_final<U1>::value, "Error!"); static_assert( is_final<U2>::value, "Error!");
— end example ]
Given the following function prototype:
template <class T> add_rvalue_reference_t<T> create() noexcept;
the predicate condition for a template specialization is_constructible<T, Args...> shall be satisfied if and only if the following variable definition would be well-formed for some invented variable t:
T t(create<Args>()...);
[ Note: These tokens are never interpreted as a function declaration. — end note ] Access checking is performed as if in a context unrelated to T and any of the Args. Only the validity of the immediate context of the variable initialization is considered. [ Note: The evaluation of the initialization can result in side effects such as the instantiation of class template specializations and function template specializations, the generation of implicitly-defined functions, and so on. Such side effects are not in the “immediate context” and can result in the program being ill-formed. — end note ]
20.10.5 Type property queries [meta.unary.prop.query]
This sub-clause contains templates that may be used to query properties of types at compile time.
| Template | Value |
|
template <class T> struct alignment_of; |
alignof(T). Requires: alignof(T) shall be a valid expression ([expr.alignof]) |
| template <class T> struct rank; | If T names an array type, an integer value representing the number of dimensions of T; otherwise, 0. |
| template <class T, unsigned I = 0> struct extent; | If T is not an array type, or if it has rank less than or equal to I, or if I is 0 and T has type “array of unknown bound of U”, then 0; otherwise, the bound ([dcl.array]) of the I'th dimension of T, where indexing of I is zero-based |
Each of these templates shall be a UnaryTypeTrait ([meta.rqmts]) with a BaseCharacteristic of integral_constant<size_t, Value>.
[ Example:
// the following assertions hold:
assert(rank<int>::value == 0);
assert(rank<int[2]>::value == 1);
assert(rank<int[][4]>::value == 2);
— end example ]
[ Example:
// the following assertions hold:
assert(extent<int>::value == 0);
assert(extent<int[2]>::value == 2);
assert(extent<int[2][4]>::value == 2);
assert(extent<int[][4]>::value == 0);
assert((extent<int, 1>::value) == 0);
assert((extent<int[2], 1>::value) == 0);
assert((extent<int[2][4], 1>::value) == 4);
assert((extent<int[][4], 1>::value) == 4);
— end example ]
20.10.6 Relationships between types [meta.rel]
This sub-clause contains templates that may be used to query relationships between types at compile time.
Each of these templates shall be a BinaryTypeTrait ([meta.rqmts]) with a BaseCharacteristic of true_type if the corresponding condition is true, otherwise false_type.
| Template | Condition | Comments |
|
template <class T, class U> struct is_same; | T and U name the same type with the same cv-qualifications | |
| template <class Base, class Derived> struct is_base_of; | Base is a base class of Derived (Clause [class.derived]) without regard to cv-qualifiers or Base and Derived are not unions and name the same class type without regard to cv-qualifiers | If Base and Derived are non-union class types and are different types (ignoring possible cv-qualifiers) then Derived shall be a complete type. [ Note: Base classes that are private, protected, or ambiguous are, nonetheless, base classes. — end note ] |
| template <class From, class To> struct is_convertible; | see below | From and To shall be complete types, arrays of unknown bound, or (possibly cv-qualified) void types. |
[ Example:
struct B {};
struct B1 : B {};
struct B2 : B {};
struct D : private B1, private B2 {};
is_base_of<B, D>::value // true
is_base_of<const B, D>::value // true
is_base_of<B, const D>::value // true
is_base_of<B, const B>::value // true
is_base_of<D, B>::value // false
is_base_of<B&, D&>::value // false
is_base_of<B[3], D[3]>::value // false
is_base_of<int, int>::value // false
— end example ]
Given the following function prototype:
template <class T> add_rvalue_reference_t<T> create() noexcept;
the predicate condition for a template specialization is_convertible<From, To> shall be satisfied if and only if the return expression in the following code would be well-formed, including any implicit conversions to the return type of the function:
To test() {
return create<From>();
}
[ Note: This requirement gives well defined results for reference types, void types, array types, and function types. — end note ] Access checking is performed as if in a context unrelated to To and From. Only the validity of the immediate context of the expression of the return-statement (including conversions to the return type) is considered. [ Note: The evaluation of the conversion can result in side effects such as the instantiation of class template specializations and function template specializations, the generation of implicitly-defined functions, and so on. Such side effects are not in the “immediate context” and can result in the program being ill-formed. — end note ]
20.10.7 Transformations between types [meta.trans]
This sub-clause contains templates that may be used to transform one type to another following some predefined rule.
Each of the templates in this subclause shall be a TransformationTrait ([meta.rqmts]).
20.10.7.1 Const-volatile modifications [meta.trans.cv]
| Template | Comments |
|
template <class T> struct remove_const; | The member typedef type shall name the same type as T except that any top-level const-qualifier has been removed. [ Example: remove_const_t<const volatile int> evaluates to volatile int, whereas remove_const_t<const int*> evaluates to const int*. — end example ] |
|
template <class T> struct remove_volatile; | The member typedef type shall name the same type as T except that any top-level volatile-qualifier has been removed. [ Example: remove_volatile_t<const volatile int> evaluates to const int, whereas remove_volatile_t<volatile int*> evaluates to volatile int*. — end example ] |
|
template <class T> struct remove_cv; | The member typedef type shall be the same as T except that any top-level cv-qualifier has been removed. [ Example: remove_cv_t<const volatile int> evaluates to int, whereas remove_cv_t<const volatile int*> evaluates to const volatile int*. — end example ] |
|
template <class T> struct add_const; | If T is a reference, function, or top-level const-qualified type, then type shall name the same type as T, otherwise T const. |
|
template <class T> struct add_volatile; | If T is a reference, function, or top-level volatile-qualified type, then type shall name the same type as T, otherwise T volatile. |
|
template <class T> struct add_cv; | The member typedef type shall name the same type as add_const_t<add_volatile_t<T>>. |
20.10.7.2 Reference modifications [meta.trans.ref]
| Template | Comments |
|
template <class T> struct remove_reference; | If T has type “reference to T1” then the member typedef type shall name T1; otherwise, type shall name T. |
| template <class T> struct add_lvalue_reference; | If T names an object or function type then the member typedef type shall name T&; otherwise, if T names a type “rvalue reference to T1” then the member typedef type shall name T1&; otherwise, type shall name T. |
| template <class T> struct add_rvalue_reference; | If T names an object or function type then the member typedef type shall name T&&; otherwise, type shall name T. [ Note: This rule reflects the semantics of reference collapsing ([dcl.ref]). For example, when a type T names a type T1&, the type add_rvalue_reference_t<T> is not an rvalue reference. — end note ] |
20.10.7.3 Sign modifications [meta.trans.sign]
| Template | Comments |
|
template <class T> struct make_signed; |
If T names a (possibly cv-qualified) signed integer
type ([basic.fundamental]) then the member typedef
type shall name the type T; otherwise,
if T names a (possibly cv-qualified) unsigned integer
type then type shall name the corresponding
signed integer type, with the same cv-qualifiers as T;
otherwise, type shall name the signed integer type with smallest
rank ([conv.rank]) for which
sizeof(T) == sizeof(type), with the same
cv-qualifiers as T. Requires: T shall be a (possibly cv-qualified) integral type or enumeration but not a bool type. |
|
template <class T> struct make_unsigned; |
If T names a (possibly cv-qualified) unsigned integer
type ([basic.fundamental]) then the member typedef
type shall name the type T; otherwise,
if T names a (possibly cv-qualified) signed integer
type then type shall name the corresponding
unsigned integer type, with the same cv-qualifiers as T;
otherwise, type shall name the unsigned integer type with smallest
rank ([conv.rank]) for which
sizeof(T) == sizeof(type), with the same
cv-qualifiers as T. Requires: T shall be a (possibly cv-qualified) integral type or enumeration but not a bool type. |
20.10.7.4 Array modifications [meta.trans.arr]
| Template | Comments |
|
template <class T> struct remove_extent; | If T names a type “array of U”, the member typedef type shall be U, otherwise T. [ Note: For multidimensional arrays, only the first array dimension is removed. For a type “array of const U”, the resulting type is const U. — end note ] |
|
template <class T> struct remove_all_extents; | If T is “multi-dimensional array of U”, the resulting member typedef type is U, otherwise T. |
[Example
// the following assertions hold:
assert((is_same<remove_extent_t<int>, int>::value));
assert((is_same<remove_extent_t<int[2]>, int>::value));
assert((is_same<remove_extent_t<int[2][3]>, int[3]>::value));
assert((is_same<remove_extent_t<int[][3]>, int[3]>::value));
— end example ]
[Example
// the following assertions hold:
assert((is_same<remove_all_extents_t<int>, int>::value));
assert((is_same<remove_all_extents_t<int[2]>, int>::value));
assert((is_same<remove_all_extents_t<int[2][3]>, int>::value));
assert((is_same<remove_all_extents_t<int[][3]>, int>::value));
— end example ]
20.10.7.5 Pointer modifications [meta.trans.ptr]
| Template | Comments |
|
template <class T> struct remove_pointer; | If T has type “(possibly cv-qualified) pointer to T1” then the member typedef type shall name T1; otherwise, it shall name T. |
|
template <class T> struct add_pointer; | The member typedef type shall name the same type as remove_reference_t<T>*. |
20.10.7.6 Other transformations [meta.trans.other]
| Template | Condition | Comments |
|
template <std::size_t Len, std::size_t Align = default-alignment> struct aligned_storage; | Len shall not be zero. Align shall be equal to alignof(T) for some type T or to default-alignment. | The value of default-alignment shall be the most stringent alignment requirement for any C++ object type whose size is no greater than Len ([basic.types]). The member typedef type shall be a POD type suitable for use as uninitialized storage for any object whose size is at most Len and whose alignment is a divisor of Align. |
| template <std::size_t Len, class... Types> struct aligned_union; | At least one type is provided. | The member typedef type shall be a POD type suitable for use as uninitialized storage for any object whose type is listed in Types; its size shall be at least Len. The static member alignment_value shall be an integral constant of type std::size_t whose value is the strictest alignment of all types listed in Types. |
| template <class T> struct decay; | Let U be remove_reference_t<T>. If is_array<U>::value is true, the member typedef type shall equal remove_extent_t<U>*. If is_function<U>::value is true, the member typedef type shall equal add_pointer_t<U>. Otherwise the member typedef type equals remove_cv_t<U>. [ Note: This behavior is similar to the lvalue-to-rvalue ([conv.lval]), array-to-pointer ([conv.array]), and function-to-pointer ([conv.func]) conversions applied when an lvalue expression is used as an rvalue, but also strips cv-qualifiers from class types in order to more closely model by-value argument passing. — end note ] | |
| template <bool B, class T = void> struct enable_if; | If B is true, the member typedef type shall equal T; otherwise, there shall be no member type. | |
| template <bool B, class T, class F> struct conditional; | If B is true, the member typedef type shall equal T. If B is false, the member typedef type shall equal F. | |
| template <class... T> struct common_type; | The member typedef type shall be defined as set out below. All types in the parameter pack T shall be complete or (possibly cv) void. A program may specialize this trait if at least one template parameter in the specialization is a user-defined type. [ Note: Such specializations are needed when only explicit conversions are desired among the template arguments. — end note ] | |
| template <class T> struct underlying_type; | T shall be an enumeration type ([dcl.enum]) | The member typedef type shall name the underlying type of T. |
| template <class Fn, class... ArgTypes> struct result_of<Fn(ArgTypes...)>; | Fn and all types in the parameter pack ArgTypes shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. | If the expression INVOKE(declval<Fn>(), declval<ArgTypes>()...) is well formed when treated as an unevaluated operand (Clause [expr]), the member typedef type shall name the type decltype(INVOKE(declval<Fn>(), declval<ArgTypes>()...)); otherwise, there shall be no member type. Access checking is performed as if in a context unrelated to Fn and ArgTypes. Only the validity of the immediate context of the expression is considered. [ Note: The compilation of the expression can result in side effects such as the instantiation of class template specializations and function template specializations, the generation of implicitly-defined functions, and so on. Such side effects are not in the “immediate context” and can result in the program being ill-formed. — end note ] |
[ Note: A typical implementation would define aligned_storage as:
template <std::size_t Len, std::size_t Alignment>
struct aligned_storage {
typedef struct {
alignas(Alignment) unsigned char __data[Len];
} type;
};
— end note ]
It is implementation-defined whether any extended alignment is supported ([basic.align]).
The nested typedef common_type::type shall be defined as follows:
template <class ...T> struct common_type;
template <class T>
struct common_type<T> {
typedef decay_t<T> type;
};
template <class T, class U>
struct common_type<T, U> {
typedef decay_t<decltype(true ? declval<T>() : declval<U>())> type;
};
template <class T, class U, class... V>
struct common_type<T, U, V...> {
typedef common_type_t<common_type_t<T, U>, V...> type;
};
[ Example: Given these definitions:
typedef bool (&PF1)();
typedef short (*PF2)(long);
struct S {
operator PF2() const;
double operator()(char, int&);
void fn(long) const;
char data;
};
typedef void (S::*PMF)(long) const;
typedef char S::*PMD;
the following assertions will hold:
static_assert(is_same<result_of_t<S(int)>, short>::value, "Error!"); static_assert(is_same<result_of_t<S&(unsigned char, int&)>, double>::value, "Error!"); static_assert(is_same<result_of_t<PF1()>, bool>::value, "Error!"); static_assert(is_same<result_of_t<PMF(unique_ptr<S>, int)>, void>::value, "Error!"); static_assert(is_same<result_of_t<PMD(S)>, char&&>::value, "Error!"); static_assert(is_same<result_of_t<PMD(const S*)>, const char&>::value, "Error!");
— end example ]
20.11 Compile-time rational arithmetic [ratio]
20.11.1 In general [ratio.general]
This subclause describes the ratio library. It provides a class template ratio which exactly represents any finite rational number with a numerator and denominator representable by compile-time constants of type intmax_t.
Throughout this subclause, the names of template parameters are used to express type requirements. If a template parameter is named R1 or R2, and the template argument is not a specialization of the ratio template, the program is ill-formed.
20.11.2 Header <ratio> synopsis [ratio.syn]
namespace std // [ratio.ratio], class template ratio template <intmax_t N, intmax_t D = 1> class ratio; // [ratio.arithmetic], ratio arithmetic template <class R1, class R2> using ratio_add = @see below@; template <class R1, class R2> using ratio_subtract = @see below@; template <class R1, class R2> using ratio_multiply = @see below@; template <class R1, class R2> using ratio_divide = @see below@; // [ratio.comparison], ratio comparison template <class R1, class R2> struct ratio_equal; template <class R1, class R2> struct ratio_not_equal; template <class R1, class R2> struct ratio_less; template <class R1, class R2> struct ratio_less_equal; template <class R1, class R2> struct ratio_greater; template <class R1, class R2> struct ratio_greater_equal; // [ratio.si], convenience SI typedefs typedef ratio<1, 1'000'000'000'000'000'000'000'000> yocto; // see below typedef ratio<1, 1'000'000'000'000'000'000'000> zepto; // see below typedef ratio<1, 1'000'000'000'000'000'000> atto; typedef ratio<1, 1'000'000'000'000'000> femto; typedef ratio<1, 1'000'000'000'000> pico; typedef ratio<1, 1'000'000'000> nano; typedef ratio<1, 1'000'000> micro; typedef ratio<1, 1'000> milli; typedef ratio<1, 100> centi; typedef ratio<1, 10> deci; typedef ratio< 10, 1> deca; typedef ratio< 100, 1> hecto; typedef ratio< 1'000, 1> kilo; typedef ratio< 1'000'000, 1> mega; typedef ratio< 1'000'000'000, 1> giga; typedef ratio< 1'000'000'000'000, 1> tera; typedef ratio< 1'000'000'000'000'000, 1> peta; typedef ratio< 1'000'000'000'000'000'000, 1> exa; typedef ratio< 1'000'000'000'000'000'000'000, 1> zetta; // see below typedef ratio<1'000'000'000'000'000'000'000'000, 1> yotta; // see below
20.11.3 Class template ratio [ratio.ratio]
namespace std {
template <intmax_t N, intmax_t D = 1>
class ratio {
public:
static constexpr intmax_t num;
static constexpr intmax_t den;
typedef ratio<num, den> type;
};
}
If the template argument D is zero or the absolute values of either of the template arguments N and D is not representable by type intmax_t, the program is ill-formed. [ Note: These rules ensure that infinite ratios are avoided and that for any negative input, there exists a representable value of its absolute value which is positive. In a two's complement representation, this excludes the most negative value. — end note ]
20.11.4 Arithmetic on ratios [ratio.arithmetic]
Each of the alias templates ratio_add, ratio_subtract, ratio_multiply, and ratio_divide denotes the result of an arithmetic computation on two ratios R1 and R2. With X and Y computed (in the absence of arithmetic overflow) as specified by Table [tab:ratio.arithmetic], each alias denotes a ratio<U, V> such that U is the same as ratio<X, Y>::num and V is the same as ratio<X, Y>::den.
If it is not possible to represent U or V with intmax_t, the program is ill-formed. Otherwise, an implementation should yield correct values of U and V. If it is not possible to represent X or Y with intmax_t, the program is ill-formed unless the implementation yields correct values of U and V.
| Type | Value of X | Value of Y |
| ratio_add<R1, R2> | R1::num * R2::den + | R1::den * R2::den |
| R2::num * R1::den | ||
| ratio_subtract<R1, R2> | R1::num * R2::den - | R1::den * R2::den |
| R2::num * R1::den | ||
| ratio_multiply<R1, R2> | R1::num * R2::num | R1::den * R2::den |
| ratio_divide<R1, R2> | R1::num * R2::den | R1::den * R2::num |
[ Example:
static_assert(ratio_add<ratio<1,3>, ratio<1,6>>::num == 1, "1/3+1/6 == 1/2");
static_assert(ratio_add<ratio<1,3>, ratio<1,6>>::den == 2, "1/3+1/6 == 1/2");
static_assert(ratio_multiply<ratio<1,3>, ratio<3,2>>::num == 1, "1/3*3/2 == 1/2");
static_assert(ratio_multiply<ratio<1,3>, ratio<3,2>>::den == 2, "1/3*3/2 == 1/2");
// The following cases may cause the program to be ill-formed under some implementations
static_assert(ratio_add<ratio<1,INT_MAX>, ratio<1,INT_MAX>>::num == 2,
"1/MAX+1/MAX == 2/MAX");
static_assert(ratio_add<ratio<1,INT_MAX>, ratio<1,INT_MAX>>::den == INT_MAX,
"1/MAX+1/MAX == 2/MAX");
static_assert(ratio_multiply<ratio<1,INT_MAX>, ratio<INT_MAX,2>>::num == 1,
"1/MAX * MAX/2 == 1/2");
static_assert(ratio_multiply<ratio<1,INT_MAX>, ratio<INT_MAX,2>>::den == 2,
"1/MAX * MAX/2 == 1/2");
— end example ]
20.11.5 Comparison of ratios [ratio.comparison]
template <class R1, class R2> struct ratio_equal
: integral_constant<bool, see below> { };
If R1::num == R2::num and R1::den == R2::den, ratio_equal<R1,
R2> shall be derived from
integral_constant<bool, true>; otherwise it shall
be derived from integral_constant<bool, false>.
template <class R1, class R2> struct ratio_not_equal
: integral_constant<bool, !ratio_equal<R1, R2>::value> { };
template <class R1, class R2> struct ratio_less
: integral_constant<bool, see below> { };
If R1::num * R2::den < R2::num * R1::den, ratio_less<R1, R2> shall be derived from integral_constant<bool, true>; otherwise it shall be derived from integral_constant<bool, false>. Implementations may use other algorithms to compute this relationship to avoid overflow. If overflow occurs, the program is ill-formed.
template <class R1, class R2> struct ratio_less_equal
: integral_constant<bool, !ratio_less<R2, R1>::value> { };
template <class R1, class R2> struct ratio_greater
: integral_constant<bool, ratio_less<R2, R1>::value> { };
template <class R1, class R2> struct ratio_greater_equal
: integral_constant<bool, !ratio_less<R1, R2>::value> { };
20.11.6 SI types for ratio [ratio.si]
For each of the typedefs yocto, zepto, zetta, and yotta, if both of the constants used in its specification are representable by intmax_t, the typedef shall be defined; if either of the constants is not representable by intmax_t, the typedef shall not be defined.
20.12 Time utilities [time]
20.12.1 In general [time.general]
This subclause describes the chrono library ([time.syn]) and various C functions ([date.time]) that provide generally useful time utilities.
20.12.2 Header <chrono> synopsis [time.syn]
namespace std {
namespace chrono {
// [time.duration], class template duration
template <class Rep, class Period = ratio<1> > class duration;
// [time.point], class template time_point
template <class Clock, class Duration = typename Clock::duration> class time_point;
} // namespace chrono
// [time.traits.specializations] common_type specializations
template <class Rep1, class Period1, class Rep2, class Period2>
struct common_type<chrono::duration<Rep1, Period1>, chrono::duration<Rep2, Period2>>;
template <class Clock, class Duration1, class Duration2>
struct common_type<chrono::time_point<Clock, Duration1>, chrono::time_point<Clock, Duration2>>;
namespace chrono {
// [time.traits], customization traits
template <class Rep> struct treat_as_floating_point;
template <class Rep> struct duration_values;
// [time.duration.nonmember], duration arithmetic
template <class Rep1, class Period1, class Rep2, class Period2>
common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
constexpr operator+(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period1, class Rep2, class Period2>
common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
constexpr operator-(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period, class Rep2>
duration<common_type_t<Rep1, Rep2>, Period>
constexpr operator*(const duration<Rep1, Period>& d, const Rep2& s);
template <class Rep1, class Rep2, class Period>
duration<common_type_t<Rep1, Rep2>, Period>
constexpr operator*(const Rep1& s, const duration<Rep2, Period>& d);
template <class Rep1, class Period, class Rep2>
duration<common_type_t<Rep1, Rep2>, Period>
constexpr operator/(const duration<Rep1, Period>& d, const Rep2& s);
template <class Rep1, class Period1, class Rep2, class Period2>
common_type_t<Rep1, Rep2>
constexpr operator/(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period, class Rep2>
duration<common_type_t<Rep1, Rep2>, Period>
constexpr operator%(const duration<Rep1, Period>& d, const Rep2& s);
template <class Rep1, class Period1, class Rep2, class Period2>
common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
constexpr operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
// [time.duration.comparisons], duration comparisons
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator==(const duration<Rep1, Period1>& lhs,
const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator!=(const duration<Rep1, Period1>& lhs,
const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator< (const duration<Rep1, Period1>& lhs,
const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator<=(const duration<Rep1, Period1>& lhs,
const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator> (const duration<Rep1, Period1>& lhs,
const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator>=(const duration<Rep1, Period1>& lhs,
const duration<Rep2, Period2>& rhs);
// [time.duration.cast], duration_cast
template <class ToDuration, class Rep, class Period>
constexpr ToDuration duration_cast(const duration<Rep, Period>& d);
// convenience typedefs
typedef duration<signed integer type of at least 64 bits, nano> nanoseconds;
typedef duration<signed integer type of at least 55 bits, micro> microseconds;
typedef duration<signed integer type of at least 45 bits, milli> milliseconds;
typedef duration<signed integer type of at least 35 bits > seconds;
typedef duration<signed integer type of at least 29 bits, ratio< 60>> minutes;
typedef duration<signed integer type of at least 23 bits, ratio<3600>> hours;
// [time.point.nonmember], time_point arithmetic
template <class Clock, class Duration1, class Rep2, class Period2>
constexpr time_point<Clock, common_type_t<Duration1, duration<Rep2, Period2>>>
operator+(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);
template <class Rep1, class Period1, class Clock, class Duration2>
constexpr time_point<Clock, common_type_t<duration<Rep1, Period1>, Duration2>>
operator+(const duration<Rep1, Period1>& lhs, const time_point<Clock, Duration2>& rhs);
template <class Clock, class Duration1, class Rep2, class Period2>
constexpr time_point<Clock, common_type_t<Duration1, duration<Rep2, Period2>>>
operator-(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);
template <class Clock, class Duration1, class Duration2>
constexpr common_type_t<Duration1, Duration2>
operator-(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
// [time.point.comparisons] time_point comparisons
template <class Clock, class Duration1, class Duration2>
constexpr bool operator==(const time_point<Clock, Duration1>& lhs,
const time_point<Clock, Duration2>& rhs);
template <class Clock, class Duration1, class Duration2>
constexpr bool operator!=(const time_point<Clock, Duration1>& lhs,
const time_point<Clock, Duration2>& rhs);
template <class Clock, class Duration1, class Duration2>
constexpr bool operator< (const time_point<Clock, Duration1>& lhs,
const time_point<Clock, Duration2>& rhs);
template <class Clock, class Duration1, class Duration2>
constexpr bool operator<=(const time_point<Clock, Duration1>& lhs,
const time_point<Clock, Duration2>& rhs);
template <class Clock, class Duration1, class Duration2>
constexpr bool operator> (const time_point<Clock, Duration1>& lhs,
const time_point<Clock, Duration2>& rhs);
template <class Clock, class Duration1, class Duration2>
constexpr bool operator>=(const time_point<Clock, Duration1>& lhs,
const time_point<Clock, Duration2>& rhs);
// [time.point.cast], time_point_cast
template <class ToDuration, class Clock, class Duration>
constexpr time_point<Clock, ToDuration>
time_point_cast(const time_point<Clock, Duration>& t);
// [time.clock], clocks
class system_clock;
class steady_clock;
class high_resolution_clock;
} // namespace chrono
inline namespace literals {
inline namespace chrono_literals {
// [time.duration.literals], suffixes for duration literals
constexpr chrono::hours operator "" h(unsigned long long);
constexpr chrono::duration<unspecified, ratio<3600,1>> operator "" h(long double);
constexpr chrono::minutes operator "" min(unsigned long long);
constexpr chrono::duration<unspecified, ratio<60,1>> operator "" min(long double);
constexpr chrono::seconds operator "" s(unsigned long long);
constexpr chrono::duration<unspecified> operator "" s(long double);
constexpr chrono::milliseconds operator "" ms(unsigned long long);
constexpr chrono::duration<unspecified, milli> operator "" ms(long double);
constexpr chrono::microseconds operator "" us(unsigned long long);
constexpr chrono::duration<unspecified, micro> operator "" us(long double);
constexpr chrono::nanoseconds operator "" ns(unsigned long long);
constexpr chrono::duration<unspecified, nano> operator "" ns(long double);
} // namespace chrono_literals
} // namespace literals
namespace chrono {
using namespace literals::chrono_literals;
} // namespace chrono
} // namespace std
20.12.3 Clock requirements [time.clock.req]
A clock is a bundle consisting of a duration, a time_point, and a function now() to get the current time_point. The origin of the clock's time_point is referred to as the clock's epoch. A clock shall meet the requirements in Table [tab:time.clock].
In Table [tab:time.clock] C1 and C2 denote clock types. t1 and t2 are values returned by C1::now() where the call returning t1 happens before ([intro.multithread]) the call returning t2 and both of these calls occur before C1::time_point::max(). [ Note: this means C1 did not wrap around between t1 and t2. — end note ]
| Expression | Return type | Operational semantics |
| C1::rep | An arithmetic type or a class emulating an arithmetic type | The representation type of C1::duration. |
| C1::period | a specialization of ratio | The tick period of the clock in seconds. |
| C1::duration | chrono::duration<C1::rep, C1::period> | The duration type of the clock. |
| C1::time_point | chrono::time_point<C1> or chrono::time_point<C2, C1::duration> | The time_point type of the clock. C1 and C2 shall refer to the same epoch. |
| C1::is_steady | const bool | true if t1 <= t2 is always true and the time between clock ticks is constant, otherwise false. |
| C1::now() | C1::time_point | Returns a time_point object representing the current point in time. |
[ Note: The relative difference in durations between those reported by a given clock and the SI definition is a measure of the quality of implementation. — end note ]
A type TC meets the TrivialClock requirements if:
TC satisfies the Clock requirements ([time.clock.req]),
the types TC::rep, TC::duration, and TC::time_point satisfy the requirements of EqualityComparable (Table [equalitycomparable]), LessThanComparable (Table [lessthancomparable]), DefaultConstructible (Table [defaultconstructible]), CopyConstructible (Table [copyconstructible]), CopyAssignable (Table [copyassignable]), Destructible (Table [destructible]), and the requirements of numeric types ([numeric.requirements]). [ Note: this means, in particular, that operations on these types will not throw exceptions. — end note ]
lvalues of the types TC::rep, TC::duration, and TC::time_point are swappable ([swappable.requirements]),
the function TC::now() does not throw exceptions, and
the type TC::time_point::clock meets the TrivialClock requirements, recursively.
20.12.4 Time-related traits [time.traits]
20.12.4.1 treat_as_floating_point [time.traits.is_fp]
template <class Rep> struct treat_as_floating_point
: is_floating_point<Rep> { };
The duration template uses the treat_as_floating_point trait to help determine if a duration object can be converted to another duration with a different tick period. If treat_as_floating_point<Rep>::value is true, then implicit conversions are allowed among durations. Otherwise, the implicit convertibility depends on the tick periods of the durations. [ Note: The intention of this trait is to indicate whether a given class behaves like a floating-point type, and thus allows division of one value by another with acceptable loss of precision. If treat_as_floating_point<Rep>::value is false, Rep will be treated as if it behaved like an integral type for the purpose of these conversions. — end note ]
20.12.4.2 duration_values [time.traits.duration_values]
template <class Rep>
struct duration_values {
public:
static constexpr Rep zero();
static constexpr Rep min();
static constexpr Rep max();
};
The duration template uses the duration_values trait to construct special values of the durations representation (Rep). This is done because the representation might be a class type with behavior which requires some other implementation to return these special values. In that case, the author of that class type should specialize duration_values to return the indicated values.
Returns: Rep(0). [ Note: Rep(0) is specified instead of Rep() because Rep() may have some other meaning, such as an uninitialized value. — end note ]
Remark: The value returned shall be the additive identity.
Returns: numeric_limits<Rep>::lowest().
Remark: The value returned shall compare less than or equal to zero().
Returns: numeric_limits<Rep>::max().
Remark: The value returned shall compare greater than zero().
20.12.4.3 Specializations of common_type [time.traits.specializations]
template <class Rep1, class Period1, class Rep2, class Period2>
struct common_type<chrono::duration<Rep1, Period1>, chrono::duration<Rep2, Period2>> {
typedef chrono::duration<common_type_t<Rep1, Rep2>, see below> type;
};
The period of the duration indicated by this specialization of common_type shall be the greatest common divisor of Period1 and Period2. [ Note: This can be computed by forming a ratio of the greatest common divisor of Period1::num and Period2::num and the least common multiple of Period1::den and Period2::den. — end note ]
[ Note: The typedef name type is a synonym for the duration with the largest tick period possible where both duration arguments will convert to it without requiring a division operation. The representation of this type is intended to be able to hold any value resulting from this conversion with no truncation error, although floating-point durations may have round-off errors. — end note ]
template <class Clock, class Duration1, class Duration2>
struct common_type<chrono::time_point<Clock, Duration1>, chrono::time_point<Clock, Duration2>> {
typedef chrono::time_point<Clock, common_type_t<Duration1, Duration2>> type;
};
The common type of two time_point types is a time_point with the same clock as the two types and the common type of their two durations.
20.12.5 Class template duration [time.duration]
A duration type measures time between two points in time (time_points). A duration has a representation which holds a count of ticks and a tick period. The tick period is the amount of time which occurs from one tick to the next, in units of seconds. It is expressed as a rational constant using the template ratio.
template <class Rep, class Period = ratio<1>>
class duration {
public:
typedef Rep rep;
typedef Period period;
private:
rep rep_; // exposition only
public:
// [time.duration.cons], construct/copy/destroy:
constexpr duration() = default;
template <class Rep2>
constexpr explicit duration(const Rep2& r);
template <class Rep2, class Period2>
constexpr duration(const duration<Rep2, Period2>& d);
~duration() = default;
duration(const duration&) = default;
duration& operator=(const duration&) = default;
// [time.duration.observer], observer:
constexpr rep count() const;
// [time.duration.arithmetic], arithmetic:
constexpr duration operator+() const;
constexpr duration operator-() const;
duration& operator++();
duration operator++(int);
duration& operator--();
duration operator--(int);
duration& operator+=(const duration& d);
duration& operator-=(const duration& d);
duration& operator*=(const rep& rhs);
duration& operator/=(const rep& rhs);
duration& operator%=(const rep& rhs);
duration& operator%=(const duration& rhs);
// [time.duration.special], special values:
static constexpr duration zero();
static constexpr duration min();
static constexpr duration max();
};
Requires: Rep shall be an arithmetic type or a class emulating an arithmetic type.
Remarks: If duration is instantiated with a duration type for the template argument Rep, the program is ill-formed.
Remarks: If Period is not a specialization of ratio, the program is ill-formed.
Remarks: If Period::num is not positive, the program is ill-formed.
Requires: Members of duration shall not throw exceptions other than those thrown by the indicated operations on their representations.
Remarks: The defaulted copy constructor of duration shall be a constexpr function if and only if the required initialization of the member rep_ for copy and move, respectively, would satisfy the requirements for a constexpr function.
[ Example:
duration<long, ratio<60>> d0; // holds a count of minutes using a long duration<long long, milli> d1; // holds a count of milliseconds using a long long duration<double, ratio<1, 30>> d2; // holds a count with a tick period ofof a second // (30 Hz) using a double
— end example ]
20.12.5.1 duration constructors [time.duration.cons]
template <class Rep2>
constexpr explicit duration(const Rep2& r);
Remarks: This constructor shall not participate in overload resolution unless Rep2 is implicitly convertible to rep and
treat_as_floating_point<rep>::value is true or
treat_as_floating_point<Rep2>::value is false.
[ Example:
duration<int, milli> d(3); // OK duration<int, milli> d(3.5); // error
— end example ]
Effects: Constructs an object of type duration.
Postcondition: count() == static_cast<rep>(r).
template <class Rep2, class Period2>
constexpr duration(const duration<Rep2, Period2>& d);
Remarks: This constructor shall not participate in overload resolution unless no overflow is induced in the conversion and treat_as_floating_point<rep>::value is true or both ratio_divide<Period2, period>::den is 1 and treat_as_floating_point<Rep2>::value is false. [ Note: This requirement prevents implicit truncation error when converting between integral-based duration types. Such a construction could easily lead to confusion about the value of the duration. — end note ] [ Example:
duration<int, milli> ms(3); duration<int, micro> us = ms; // OK duration<int, milli> ms2 = us; // error
— end example ]
Effects: Constructs an object of type duration, constructing rep_ from
duration_cast<duration>(d).count().
20.12.5.3 duration arithmetic [time.duration.arithmetic]
constexpr duration operator+() const;
Returns: *this.
constexpr duration operator-() const;
Returns: duration(-rep_);.
Effects: ++rep_.
Returns: *this.
Returns: duration(rep_++);.
Effects: --rep_.
Returns: *this.
Returns: duration(rep_--);.
duration& operator+=(const duration& d);
Effects: rep_ += d.count().
Returns: *this.
duration& operator-=(const duration& d);
Effects: rep_ -= d.count().
Returns: *this.
duration& operator*=(const rep& rhs);
Effects: rep_ *= rhs.
Returns: *this.
duration& operator/=(const rep& rhs);
Effects: rep_ /= rhs.
Returns: *this.
duration& operator%=(const rep& rhs);
Effects: rep_ %= rhs.
Returns: *this.
duration& operator%=(const duration& rhs);
Effects: rep_ %= rhs.count().
Returns: *this.
20.12.5.4 duration special values [time.duration.special]
static constexpr duration zero();
Returns: duration(duration_values<rep>::zero()).
static constexpr duration min();
Returns: duration(duration_values<rep>::min()).
static constexpr duration max();
Returns: duration(duration_values<rep>::max()).
20.12.5.5 duration non-member arithmetic [time.duration.nonmember]
In the function descriptions that follow, CD represents the return type of the function. CR(A,B) represents common_type_t<A, B>.
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
operator+(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CD(CD(lhs).count() + CD(rhs).count()).
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
operator-(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CD(CD(lhs).count() - CD(rhs).count()).
template <class Rep1, class Period, class Rep2>
constexpr duration<common_type_t<Rep1, Rep2>, Period>
operator*(const duration<Rep1, Period>& d, const Rep2& s);
Remarks: This operator shall not participate in overload resolution unless Rep2 is implicitly convertible to CR(Rep1, Rep2).
Returns: CD(CD(d).count() * s).
template <class Rep1, class Rep2, class Period>
constexpr duration<common_type_t<Rep1, Rep2>, Period>
operator*(const Rep1& s, const duration<Rep2, Period>& d);
Remarks: This operator shall not participate in overload resolution unless Rep1 is implicitly convertible to CR(Rep1, Rep2).
Returns: d * s.
template <class Rep1, class Period, class Rep2>
constexpr duration<common_type_t<Rep1, Rep2>, Period>
operator/(const duration<Rep1, Period>& d, const Rep2& s);
Remarks: This operator shall not participate in overload resolution unless Rep2 is implicitly convertible to CR(Rep1, Rep2) and Rep2 is not an instantiation of duration.
Returns: CD(CD(d).count() / s).
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr common_type_t<Rep1, Rep2>
operator/(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CD(lhs).count() / CD(rhs).count().
template <class Rep1, class Period, class Rep2>
constexpr duration<common_type_t<Rep1, Rep2>, Period>
operator%(const duration<Rep1, Period>& d, const Rep2& s);
Remarks: This operator shall not participate in overload resolution unless Rep2 is implicitly convertible to CR(Rep1, Rep2) and Rep2 is not an instantiation of duration.
Returns: CD(CD(d).count() % s).
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr common_type_t<duration<Rep1, Period1>, duration<Rep2, Period2>>
operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CD(CD(lhs).count() % CD(rhs).count()).
20.12.5.6 duration comparisons [time.duration.comparisons]
In the function descriptions that follow, CT represents common_type_t<A, B>, where A and B are the types of the two arguments to the function.
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator==(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CT(lhs).count() == CT(rhs).count().
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator!=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: !(lhs == rhs).
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator<(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CT(lhs).count() < CT(rhs).count().
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator<=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: !(rhs < lhs).
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator>(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: rhs < lhs.
template <class Rep1, class Period1, class Rep2, class Period2>
constexpr bool operator>=(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: !(lhs < rhs).
20.12.5.7 duration_cast [time.duration.cast]
template <class ToDuration, class Rep, class Period>
constexpr ToDuration duration_cast(const duration<Rep, Period>& d);
Remarks: This function shall not participate in overload resolution unless ToDuration is an instantiation of duration.
Returns: Let CF be ratio_divide<Period, typename ToDuration::period>, and CR be common_type< typename ToDuration::rep, Rep, intmax_t>::type.
If CF::num == 1 and CF::den == 1, returns
ToDuration(static_cast<typename ToDuration::rep>(d.count()))
otherwise, if CF::num != 1 and CF::den == 1, returns
ToDuration(static_cast<typename ToDuration::rep>( static_cast<CR>(d.count()) * static_cast<CR>(CF::num)))
otherwise, if CF::num == 1 and CF::den != 1, returns
ToDuration(static_cast<typename ToDuration::rep>( static_cast<CR>(d.count()) / static_cast<CR>(CF::den)))
otherwise, returns
ToDuration(static_cast<typename ToDuration::rep>( static_cast<CR>(d.count()) * static_cast<CR>(CF::num) / static_cast<CR>(CF::den)))
Notes: This function does not use any implicit conversions; all conversions are done with static_cast. It avoids multiplications and divisions when it is known at compile time that one or more arguments is 1. Intermediate computations are carried out in the widest representation and only converted to the destination representation at the final step.
20.12.5.8 Suffixes for duration literals [time.duration.literals]
This section describes literal suffixes for constructing duration literals. The suffixes h, min, s, ms, us, ns denote duration values of the corresponding types hours, minutes, seconds, milliseconds, microseconds, and nanoseconds respectively if they are applied to integral literals.
If any of these suffixes are applied to a floating point literal the result is a chrono::duration literal with an unspecified floating point representation.
If any of these suffixes are applied to an integer literal and the resulting chrono::duration value cannot be represented in the result type because of overflow, the program is ill-formed.
[ Example: The following code shows some duration literals.
using namespace std::chrono_literals; auto constexpr aday=24h; auto constexpr lesson=45min; auto constexpr halfanhour=0.5h;
— end example ]
constexpr chrono::hours operator "" h(unsigned long long hours);
constexpr chrono::duration<unspecified, ratio<3600,1>> operator "" h(long double hours);
Returns: A duration literal representing hours hours.
constexpr chrono::minutes operator "" min(unsigned long long minutes);
constexpr chrono::duration<unspecified, ratio<60,1>> operator "" min(long double minutes);
Returns: A duration literal representing minutes minutes.
constexpr chrono::seconds operator "" s(unsigned long long sec);
constexpr chrono::duration<unspecified> operator "" s(long double sec);
Returns: A duration literal representing sec seconds.
[ Note: The same suffix s is used for basic_string but there is no conflict, since duration suffixes apply to numbers and string literal suffixes apply to character array literals. — end note ]
constexpr chrono::milliseconds operator "" ms(unsigned long long msec);
constexpr chrono::duration<unspecified, milli> operator "" ms(long double msec);
Returns: A duration literal representing msec milliseconds.
constexpr chrono::microseconds operator "" us(unsigned long long usec);
constexpr chrono::duration<unspecified, micro> operator "" us(long double usec);
Returns: A duration literal representing usec microseconds.
constexpr chrono::nanoseconds operator "" ns(unsigned long long nsec);
constexpr chrono::duration<unspecified, nano> operator "" ns(long double nsec);
Returns: A duration literal representing nsec nanoseconds.
20.12.6 Class template time_point [time.point]
template <class Clock, class Duration = typename Clock::duration>
class time_point {
public:
typedef Clock clock;
typedef Duration duration;
typedef typename duration::rep rep;
typedef typename duration::period period;
private:
duration d_; // exposition only
public:
// [time.point.cons], construct:
constexpr time_point(); // has value epoch
constexpr explicit time_point(const duration& d); // same as time_point() + d
template <class Duration2>
constexpr time_point(const time_point<clock, Duration2>& t);
// [time.point.observer], observer:
constexpr duration time_since_epoch() const;
// [time.point.arithmetic], arithmetic:
time_point& operator+=(const duration& d);
time_point& operator-=(const duration& d);
// [time.point.special], special values:
static constexpr time_point min();
static constexpr time_point max();
};
Clock shall meet the Clock requirements ([time.clock]).
If Duration is not an instance of duration, the program is ill-formed.
20.12.6.1 time_point constructors [time.point.cons]
Effects: Constructs an object of type time_point, initializing d_ with duration::zero(). Such a time_point object represents the epoch.
constexpr explicit time_point(const duration& d);
Effects: Constructs an object of type time_point, initializing d_ with d. Such a time_point object represents the epoch + d.
template <class Duration2>
constexpr time_point(const time_point<clock, Duration2>& t);
Remarks: This constructor shall not participate in overload resolution unless Duration2 is implicitly convertible to duration.
Effects: Constructs an object of type time_point, initializing d_ with t.time_since_epoch().
20.12.6.2 time_point observer [time.point.observer]
constexpr duration time_since_epoch() const;
Returns: d_.
20.12.6.3 time_point arithmetic [time.point.arithmetic]
time_point& operator+=(const duration& d);
Effects: d_ += d.
Returns: *this.
time_point& operator-=(const duration& d);
Effects: d_ -= d.
Returns: *this.
20.12.6.4 time_point special values [time.point.special]
static constexpr time_point min();
Returns: time_point(duration::min()).
static constexpr time_point max();
Returns: time_point(duration::max()).
20.12.6.5 time_point non-member arithmetic [time.point.nonmember]
template <class Clock, class Duration1, class Rep2, class Period2>
constexpr time_point<Clock, common_type_t<Duration1, duration<Rep2, Period2>>>
operator+(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: CT(lhs.time_since_epoch() + rhs), where CT is the type of the return value.
template <class Rep1, class Period1, class Clock, class Duration2>
constexpr time_point<Clock, common_type_t<duration<Rep1, Period1>, Duration2>>
operator+(const duration<Rep1, Period1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: rhs + lhs.
template <class Clock, class Duration1, class Rep2, class Period2>
constexpr time_point<Clock, common_type_t<Duration1, duration<Rep2, Period2>>>
operator-(const time_point<Clock, Duration1>& lhs, const duration<Rep2, Period2>& rhs);
Returns: lhs + (-rhs).
template <class Clock, class Duration1, class Duration2>
constexpr common_type_t<Duration1, Duration2>
operator-(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: lhs.time_since_epoch() - rhs.time_since_epoch().
20.12.6.6 time_point comparisons [time.point.comparisons]
template <class Clock, class Duration1, class Duration2>
constexpr bool operator==(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: lhs.time_since_epoch() == rhs.time_since_epoch().
template <class Clock, class Duration1, class Duration2>
constexpr bool operator!=(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: !(lhs == rhs).
template <class Clock, class Duration1, class Duration2>
constexpr bool operator<(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: lhs.time_since_epoch() < rhs.time_since_epoch().
template <class Clock, class Duration1, class Duration2>
constexpr bool operator<=(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: !(rhs < lhs).
template <class Clock, class Duration1, class Duration2>
constexpr bool operator>(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: rhs < lhs.
template <class Clock, class Duration1, class Duration2>
constexpr bool operator>=(const time_point<Clock, Duration1>& lhs, const time_point<Clock, Duration2>& rhs);
Returns: !(lhs < rhs).
20.12.6.7 time_point_cast [time.point.cast]
template <class ToDuration, class Clock, class Duration>
constexpr time_point<Clock, ToDuration>
time_point_cast(const time_point<Clock, Duration>& t);
Remarks: This function shall not participate in overload resolution unless ToDuration is an instantiation of duration.
Returns: time_point<Clock, ToDuration>(duration_cast<ToDuration>(t.time_since_epoch())).
20.12.7 Clocks [time.clock]
The types defined in this subclause shall satisfy the TrivialClock requirements ([time.clock.req]).
20.12.7.1 Class system_clock [time.clock.system]
Objects of class system_clock represent wall clock time from the system-wide realtime clock.
class system_clock {
public:
typedef see below rep;
typedef ratio<unspecified, unspecified> period;
typedef chrono::duration<rep, period> duration;
typedef chrono::time_point<system_clock> time_point;
static constexpr bool is_steady = unspecified;
static time_point now() noexcept;
// Map to C API
static time_t to_time_t (const time_point& t) noexcept;
static time_point from_time_t(time_t t) noexcept;
};
Requires: system_clock::duration::min() < system_clock::duration::zero() shall be true. [ Note: This implies that rep is a signed type. — end note ]
static time_t to_time_t(const time_point& t) noexcept;
static time_point from_time_t(time_t t) noexcept;
20.12.7.2 Class steady_clock [time.clock.steady]
Objects of class steady_clock represent clocks for which values of time_point never decrease as physical time advances and for which values of time_point advance at a steady rate relative to real time. That is, the clock may not be adjusted.
class steady_clock {
public:
typedef unspecified rep;
typedef ratio<unspecified, unspecified> period;
typedef chrono::duration<rep, period> duration;
typedef chrono::time_point<unspecified, duration> time_point;
static constexpr bool is_steady = true;
static time_point now() noexcept;
};
20.12.7.3 Class high_resolution_clock [time.clock.hires]
Objects of class high_resolution_clock represent clocks with the shortest tick period. high_resolution_clock may be a synonym for system_clock or steady_clock.
class high_resolution_clock {
public:
typedef unspecified rep;
typedef ratio<unspecified, unspecified> period;
typedef chrono::duration<rep, period> duration;
typedef chrono::time_point<unspecified, duration> time_point;
static constexpr bool is_steady = unspecified;
static time_point now() noexcept;
};
20.12.8 Date and time functions [date.time]
Table [tab:util.hdr.ctime] describes the header <ctime>.
| Type | Name(s) | |||
| Macros: | NULL | CLOCKS_PER_SEC | ||
| Types: | size_t | clock_t | time_t | |
| Struct: | tm | |||
| Functions: | ||||
| asctime | clock | difftime | localtime | strftime |
| ctime | gmtime | mktime | time | |
The contents are the same as the Standard C library header <time.h>.232 The functions asctime, ctime, gmtime, and localtime are not required to avoid data races ([res.on.data.races]).
See also: ISO C Clause 7.12, Amendment 1 Clause 4.6.4.
strftime supports the C conversion specifiers C, D, e, F, g, G, h, r, R, t, T, u, V, and z, and the modifiers E and O.
20.13 Class template scoped_allocator_adaptor [allocator.adaptor]
20.13.1 Header <scoped_allocator> synopsis [allocator.adaptor.syn]
// scoped allocator adaptor
template <class OuterAlloc, class... InnerAlloc>
class scoped_allocator_adaptor;
template <class OuterA1, class OuterA2, class... InnerAllocs>
bool operator==(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
template <class OuterA1, class OuterA2, class... InnerAllocs>
bool operator!=(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
The class template scoped_allocator_adaptor is an allocator template that specifies the memory resource (the outer allocator) to be used by a container (as any other allocator does) and also specifies an inner allocator resource to be passed to the constructor of every element within the container. This adaptor is instantiated with one outer and zero or more inner allocator types. If instantiated with only one allocator type, the inner allocator becomes the scoped_allocator_adaptor itself, thus using the same allocator resource for the container and every element within the container and, if the elements themselves are containers, each of their elements recursively. If instantiated with more than one allocator, the first allocator is the outer allocator for use by the container, the second allocator is passed to the constructors of the container's elements, and, if the elements themselves are containers, the third allocator is passed to the elements' elements, and so on. If containers are nested to a depth greater than the number of allocators, the last allocator is used repeatedly, as in the single-allocator case, for any remaining recursions. [ Note: The scoped_allocator_adaptor is derived from the outer allocator type so it can be substituted for the outer allocator type in most expressions. — end note ]
namespace std {
template <class OuterAlloc, class... InnerAllocs>
class scoped_allocator_adaptor : public OuterAlloc {
private:
typedef allocator_traits<OuterAlloc> OuterTraits; // exposition only
scoped_allocator_adaptor<InnerAllocs...> inner; // exposition only
public:
typedef OuterAlloc outer_allocator_type;
typedef see below inner_allocator_type;
typedef typename OuterTraits::value_type value_type;
typedef typename OuterTraits::size_type size_type;
typedef typename OuterTraits::difference_type difference_type;
typedef typename OuterTraits::pointer pointer;
typedef typename OuterTraits::const_pointer const_pointer;
typedef typename OuterTraits::void_pointer void_pointer;
typedef typename OuterTraits::const_void_pointer const_void_pointer;
typedef see below propagate_on_container_copy_assignment;
typedef see below propagate_on_container_move_assignment;
typedef see below propagate_on_container_swap;
template <class Tp>
struct rebind {
typedef scoped_allocator_adaptor<
OuterTraits::template rebind_alloc<Tp>, InnerAllocs...> other;
};
scoped_allocator_adaptor();
template <class OuterA2>
scoped_allocator_adaptor(OuterA2&& outerAlloc,
const InnerAllocs&... innerAllocs) noexcept;
scoped_allocator_adaptor(const scoped_allocator_adaptor& other) noexcept;
scoped_allocator_adaptor(scoped_allocator_adaptor&& other) noexcept;
template <class OuterA2>
scoped_allocator_adaptor(
const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& other) noexcept;
template <class OuterA2>
scoped_allocator_adaptor(
scoped_allocator_adaptor<OuterA2, InnerAllocs...>&& other) noexcept;
~scoped_allocator_adaptor();
inner_allocator_type& inner_allocator() noexcept;
const inner_allocator_type& inner_allocator() const noexcept;
outer_allocator_type& outer_allocator() noexcept;
const outer_allocator_type& outer_allocator() const noexcept;
pointer allocate(size_type n);
pointer allocate(size_type n, const_void_pointer hint);
void deallocate(pointer p, size_type n);
size_type max_size() const;
template <class T, class... Args>
void construct(T* p, Args&&... args);
template <class T1, class T2, class... Args1, class... Args2>
void construct(pair<T1, T2>* p, piecewise_construct_t,
tuple<Args1...> x, tuple<Args2...> y);
template <class T1, class T2>
void construct(pair<T1, T2>* p);
template <class T1, class T2, class U, class V>
void construct(pair<T1, T2>* p, U&& x, V&& y);
template <class T1, class T2, class U, class V>
void construct(pair<T1, T2>* p, const pair<U, V>& x);
template <class T1, class T2, class U, class V>
void construct(pair<T1, T2>* p, pair<U, V>&& x);
template <class T>
void destroy(T* p);
scoped_allocator_adaptor select_on_container_copy_construction() const;
};
template <class OuterA1, class OuterA2, class... InnerAllocs>
bool operator==(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
template <class OuterA1, class OuterA2, class... InnerAllocs>
bool operator!=(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
}
20.13.2 Scoped allocator adaptor member types [allocator.adaptor.types]
typedef see below inner_allocator_type;
Type: scoped_allocator_adaptor<OuterAlloc> if sizeof...(InnerAllocs) is
zero; otherwise,
scoped_allocator_adaptor<InnerAllocs...>.
typedef see below propagate_on_container_copy_assignment;
Type: true_type if allocator_traits<A>::propagate_on_container_copy_assignment::value is true for any A in the set of OuterAlloc and InnerAllocs...; otherwise, false_type.
typedef see below propagate_on_container_move_assignment;
Type: true_type if allocator_traits<A>::propagate_on_container_move_assignment::value is true for any A in the set of OuterAlloc and InnerAllocs...; otherwise, false_type.
typedef see below propagate_on_container_swap;
Type: true_type if allocator_traits<A>::propagate_on_container_swap::value is true for any A in the set of OuterAlloc and InnerAllocs...; otherwise, false_type.
20.13.3 Scoped allocator adaptor constructors [allocator.adaptor.cnstr]
Effects: value-initializes the OuterAlloc base class and the inner allocator object.
template <class OuterA2>
scoped_allocator_adaptor(OuterA2&& outerAlloc,
const InnerAllocs&... innerAllocs) noexcept;
Requires: OuterAlloc shall be constructible from OuterA2.
Effects: initializes the OuterAlloc base class with std::forward<OuterA2>(outerAlloc) and inner with innerAllocs... (hence recursively initializing each allocator within the adaptor with the corresponding allocator from the argument list).
scoped_allocator_adaptor(const scoped_allocator_adaptor& other) noexcept;
Effects: initializes each allocator within the adaptor with the corresponding allocator from other.
scoped_allocator_adaptor(scoped_allocator_adaptor&& other) noexcept;
Effects: move constructs each allocator within the adaptor with the corresponding allocator from other.
template <class OuterA2>
scoped_allocator_adaptor(const scoped_allocator_adaptor<OuterA2,
InnerAllocs...>& other) noexcept;
Requires: OuterAlloc shall be constructible from OuterA2.
Effects: initializes each allocator within the adaptor with the corresponding allocator from other.
template <class OuterA2>
scoped_allocator_adaptor(scoped_allocator_adaptor<OuterA2,
InnerAllocs...>&& other) noexcept;
Requires: OuterAlloc shall be constructible from OuterA2.
Effects: initializes each allocator within the adaptor with the corresponding allocator rvalue from other.
20.13.4 Scoped allocator adaptor members [allocator.adaptor.members]
In the construct member functions,
OUTERMOST(x) is x if x does not have an
outer_allocator() member function and
OUTERMOST(x.outer_allocator())
otherwise;
OUTERMOST_ALLOC_TRAITS(x) is
allocator_traits<decltype(OUTERMOST(x))>.
[ Note: OUTERMOST(x) and
OUTERMOST_ALLOC_TRAITS(x) are recursive operations. It
is incumbent upon the definition of outer_allocator() to ensure that the
recursion terminates. It will terminate for all instantiations of
scoped_allocator_adaptor. — end note ]
inner_allocator_type& inner_allocator() noexcept;
const inner_allocator_type& inner_allocator() const noexcept;
Returns: *this if sizeof...(InnerAllocs) is zero; otherwise, inner.
outer_allocator_type& outer_allocator() noexcept;
Returns: static_cast<OuterAlloc&>(*this).
const outer_allocator_type& outer_allocator() const noexcept;
Returns: static_cast<const OuterAlloc&>(*this).
pointer allocate(size_type n);
Returns: allocator_traits<OuterAlloc>::allocate(outer_allocator(), n).
pointer allocate(size_type n, const_void_pointer hint);
Returns: allocator_traits<OuterAlloc>::allocate(outer_allocator(), n, hint).
void deallocate(pointer p, size_type n) noexcept;
Effects: allocator_traits<OuterAlloc>::deallocate(outer_allocator(), p, n);
Returns: allocator_traits<OuterAlloc>::max_size(outer_allocator()).
template <class T, class... Args>
void construct(T* p, Args&&... args);
Effects:
If uses_allocator<T, inner_allocator_type>::value is false and is_constructible<T, Args...>::value is true, calls OUTERMOST_ALLOC_TRAITS(*this)::construct(
OUTERMOST(*this), p, std::forward<Args>(args)...).Otherwise, if uses_allocator<T, inner_allocator_type>::value is true and is_constructible<T, allocator_arg_t, inner_allocator_type, Args...>::value is true, calls OUTERMOST_ALLOC_TRAITS(*this)::construct(OUTERMOST(*this), p, allocator_arg,
inner_allocator(), std::forward<Args>(args)...).Otherwise, if uses_allocator<T, inner_allocator_type>::value is true and is_constructible<T, Args..., inner_allocator_type>::value is true, calls OUTERMOST_ALLOC_TRAITS(*this):: construct(OUTERMOST(*this), p, std::forward<Args>(args)...,
inner_allocator()).Otherwise, the program is ill-formed. [ Note: An error will result if uses_allocator evaluates to true but the specific constructor does not take an allocator. This definition prevents a silent failure to pass an inner allocator to a contained element. — end note ]
template <class T1, class T2, class... Args1, class... Args2>
void construct(pair<T1, T2>* p,piecewise_construct_t,
tuple<Args1...> x, tuple<Args2...> y);
Requires: all of the types in Args1 and Args2 shall be CopyConstructible (Table [copyconstructible]).
Effects: Constructs a tuple object xprime from x by the following rules:
If uses_allocator<T1, inner_allocator_type>::value is false and is_constructible<T1, Args1...>::value is true, then xprime is x.
Otherwise, if uses_allocator<T1, inner_allocator_type>::value is true and is_constructible<T1, allocator_arg_t, inner_allocator_type, Args1...>::value is true, then xprime is tuple_cat(tuple<allocator_arg_t, inner_allocator_type&>( allocator_arg, inner_allocator()), std::move(x)).
Otherwise, if uses_allocator<T1, inner_allocator_type>::value is true and is_constructible<T1, Args1..., inner_allocator_type>::value is true, then xprime is tuple_cat(std::move(x), tuple<inner_allocator_type&>(inner_allocator())).
Otherwise, the program is ill-formed.
and constructs a tuple object yprime from y by the following rules:
If uses_allocator<T2, inner_allocator_type>::value is false and is_constructible<T2, Args2...>::value is true, then yprime is y.
Otherwise, if uses_allocator<T2, inner_allocator_type>::value is true and is_constructible<T2, allocator_arg_t, inner_allocator_type, Args2...>::value is true, then yprime is tuple_cat(tuple<allocator_arg_t, inner_allocator_type&>( allocator_arg, inner_allocator()), std::move(y)).
Otherwise, if uses_allocator<T2, inner_allocator_type>::value is true and is_constructible<T2, Args2..., inner_allocator_type>::value is true, then yprime is tuple_cat(std::move(y), tuple<inner_allocator_type&>(inner_allocator())).
Otherwise, the program is ill-formed.
then calls OUTERMOST_ALLOC_TRAITS(*this)::construct(OUTERMOST(*this), p,
piecewise_construct, std::move(xprime), std::move(yprime)).
template <class T1, class T2>
void construct(pair<T1, T2>* p);
Effects: Equivalent to this->construct(p, piecewise_construct, tuple<>(), tuple<>()).
template <class T1, class T2, class U, class V>
void construct(pair<T1, T2>* p, U&& x, V&& y);
Effects: Equivalent to this->construct(p, piecewise_construct, forward_as_tuple(std::forward<U>(x)), forward_as_tuple(std::forward<V>(y))).
template <class T1, class T2, class U, class V>
void construct(pair<T1, T2>* p, const pair<U, V>& x);
Effects: Equivalent to this->construct(p, piecewise_construct, forward_as_tuple(x.first), forward_as_tuple(x.second)).
template <class T1, class T2, class U, class V>
void construct(pair<T1, T2>* p, pair<U, V>&& x);
Effects: Equivalent to this->construct(p, piecewise_construct, forward_as_tuple(std::forward<U>(x.first)), forward_as_tuple(std::forward<V>(x.second))).
template <class T>
void destroy(T* p);
Effects: calls OUTERMOST_ALLOC_TRAITS(*this)::destroy(OUTERMOST(*this), p).
scoped_allocator_adaptor select_on_container_copy_construction() const;
Returns: A new scoped_allocator_adaptor object where each allocator A in the adaptor is initialized from the result of calling allocator_traits<A>::select_on_container_copy_construction() on the corresponding allocator in *this.
20.13.5 Scoped allocator operators [scoped.adaptor.operators]
template <class OuterA1, class OuterA2, class... InnerAllocs>
bool operator==(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
Returns: a.outer_allocator() == b.outer_allocator() if sizeof...(InnerAllocs) is zero; otherwise, a.outer_allocator() == b.outer_allocator() && a.inner_allocator() == b.inner_allocator().
template <class OuterA1, class OuterA2, class... InnerAllocs>
bool operator!=(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
Returns: !(a == b).
20.14 Class type_index [type.index]
20.14.1 Header <typeindex> synopsis [type.index.synopsis]
namespace std {
class type_index;
template <class T> struct hash;
template<> struct hash<type_index>;
}
20.14.2 type_index overview [type.index.overview]
namespace std {
class type_index {
public:
type_index(const type_info& rhs) noexcept;
bool operator==(const type_index& rhs) const noexcept;
bool operator!=(const type_index& rhs) const noexcept;
bool operator< (const type_index& rhs) const noexcept;
bool operator<= (const type_index& rhs) const noexcept;
bool operator> (const type_index& rhs) const noexcept;
bool operator>= (const type_index& rhs) const noexcept;
size_t hash_code() const noexcept;
const char* name() const noexcept;
private:
const type_info* target; // exposition only
// Note that the use of a pointer here, rather than a reference,
// means that the default copy/move constructor and assignment
// operators will be provided and work as expected.
};
}
The class type_index provides a simple wrapper for type_info which can be used as an index type in associative containers ([associative]) and in unordered associative containers ([unord]).
20.14.3 type_index members [type.index.members]
type_index(const type_info& rhs) noexcept;
Effects: constructs a type_index object, the equivalent of target = &rhs.
bool operator==(const type_index& rhs) const noexcept;
Returns: *target == *rhs.target
bool operator!=(const type_index& rhs) const noexcept;
Returns: *target != *rhs.target
bool operator<(const type_index& rhs) const noexcept;
Returns: target->before(*rhs.target)
bool operator<=(const type_index& rhs) const noexcept;
Returns: !rhs.target->before(*target)
bool operator>(const type_index& rhs) const noexcept;
Returns: rhs.target->before(*target)
bool operator>=(const type_index& rhs) const noexcept;
Returns: !target->before(*rhs.target)
size_t hash_code() const noexcept;
Returns: target->hash_code()
const char* name() const noexcept;
Returns: target->name()
20.14.4 Hash support [type.index.hash]
template <> struct hash<type_index>;
The template specialization shall meet the requirements of class template hash ([unord.hash]). For an object index of type type_index, hash<type_index>()(index) shall evaluate to the same result as index.hash_code().